Howdy all, and might I say very interesting debate this
To try to address a few things brought forth...
1.
All characters entering the Inner Realms have indeed died first. The technical reason i've always kinda kept to myself and only in the few last days of Alangara's last run to a group of Reborns taking the debate so far out philosophically that Tarasan Trueheart had to reveal it.
Zertihn besides being God of the portefolios "Just rulership, Culture and civilisation" is as most known also HOPE itself. Seen from the perspective of divinity ( Gods ) alone , he was merely at the time he discovered the Inner Realms a DEMI POWER. As such his divine power should in itself not have been even remotely enough to actually do anything to or with these interlinked pocketplanes being...
The Icedark - Auril's domain
The Middlelands - Chauntea's domain
The Tornlands - Talos' domain
However being so many different aspects of reality, including HOPE and having an indept concept of creation, time and mass/energy itlsef from being both the Son of Xymor - dragon god of wisdom and an incarnation of the Paragon of the Silverdragons ( the very first silverdragon created/emanated by/from the raw chaos of the pre-prime of creation he intervened in what would have been otherwise the destruction and death of these 3 interlinked planes.
The main force and motivation to do this was his aspect of HOPE. To give hope where there was none...
After having helped end the war that was tearing the Inner Realms apart by "defeating" ( more likely exspelling from the plane ) the Protagonist of Chaos he actually took on the part of these Gods in the Inner Realms as they had long since abandoned and forgotten their contest and project. A project that to them above all was a learning excersise in ages and realities long lost. As he took over the roles of the three Gods to reform and reshape the Inner Realms he realised that within all portefolio's ( Gods domains ) was the spire of both hope and dispair and that he as such actually had parts of his innermost being integrated in all things divine and therefore was quite capable of mimic'ing all known Gods.
To understand Zertihn one most also realise that above all else he is a "seeker of wisdom" and while being utterly true to his word ( lawfull ) he is also extremely openminded and chaotic in nature. To him reality is the moron's view upon the world and realities (plural) the only conceot that even remotely makes any sense, all thou he is even challenging that concept fiercely.
( What he usually uses to "measure the inmeasurable" is potentiality - which may or may now be described another time )
All this however means that it was his aspect of hope that saved the Inner Realms and it was that aspect that startet to bring new souls into the realm. The reason for this was to save them from the wall of the infidels , the most ultimate dispair in the known multiverse. As such only dead souls were snatched from their infernal fate.
The reason he could do this was by explicit permission from AO, after debating many aspects of possible future's nd devellopments of AO's current multiverse. Knowledge kept strictly between him and AO. ( Actually he has debated it alot with his mentor, the Lady of Pain of Sigil, and most likely with his ost valued friend NUUL, but that is for another story ).
Needless to say Zertihn, being an extremely powerfull psionisist to the level of being one of the select few being to battle the ithilid overmind, head on face to face, in the mindscape and live to tell the tale, was more than aware of the devestating effect on a mortal, or immortal, psyche realising what fate would have been there for them. Thus he utterly removed the reality of the dispair from each and every summon. Being an immense believer in personal freedom he did not want to alter the individuals perception of the world and their own history so he merely left it for their own psyche to subconsciensly explain why they had arived. For sor some this will be minute details of what actually transpired, for other uterly figments of imagination and most again a more or less powerfull blur of the events leading up to their arival. Very few however realise they escaped deaths grip, allthough some do.
2.
The Inner Realms were originally placed as a pocket dimensions in the core of toril, thousands of miles below the Underdark. As such their lore and natural belonging was to that of the pantheon of Toril. This persisted also after Zertihn found it and after the battle with the Protagonist of Chaos rivitalized it. However as the last age of the Inner Realms ( "Alanagara Reborn" ) ended with Tarasan Trueheart revealing that there was infact only one God oversing it all and playing out the part of the others, Zertihn realised that it was time to devellop once again and also to "up the ante". Thus he completely recreated the Intire Inner realms and expanded it considerably from the 3 original continents. Also he once again broke any known universal law of divine conduct merging in the powers of both the Aspects ( exsample of one of those would be the Lady of Pain ) and divinity , sanctioned and aproved by both the Aspects and AO. Expanding upon reality in such a manner unheard of before instantly elevated Zertihn to the rank of "AO" in the Inner Realms and formidable greater power under AO, while once again breaking all rules by actually limiting himsself to function as still a demipower outside in the multiverse for reason not tied directly to the Inner Realms.
The Inner Realms, being both the "divine homeplane of Zertihn the God" and the "Centre of Hope" sports some heavy variations from "the normal realms and planes in the multiverse".
All things are much more powerfull in the Inner Realms forcing growth upon the player characters in a unseen scale in the multiverse. Thus a level 40 reborn character in the Inner Realms will be overwhelmingly powerfull outside the Inner realms. A level 40 reborn ending up in Ravenloft would be supreme in power in whatever realm he or she reached and the only "salvation" for their present rules would be their ability to expell others from their realm at will.
Thus the Inner realms match much more those of the heavens or the hells than any primeplane allthough uniqely set apart from those as well.
3.
One of the main concept in the Inner Realms is the uniqe power of mortals. Zertihn obviously encourages this growth by the intire setup of the Inner Realms but he does much more than that. Being an ever wandering seeker of wisdom Zertihn actively learns from each and every soul entering his domain. What he has long since realised is that the limitations in perception of a mortal and the here of following limited point of view is not only a limit. It is the very foundation for creating something uniqe. As such all mortals carry with them a uniqe perception of the world, a uniqe ideolegy and so forth. Zerithn's not only learns from each of these but he infact allows them to directly influence the Inner Realms - under supervision by both the Inner Realms themselves and his direct consciousness.
It is also the understanding of this knowledge that leads for mortals to be able to become reborn. As such all Reborns therefore are the prime agents of a given cause or ideolegy or specific Gods portefolio's. Most Reborns directly follow a given God and following a path that would eventually lead them to potentially become CHOSEN og said Diety. A few however stroll out upon paths unknown.
No player character may become "reborn of Zertihn" and all Reborns of him during the existance of the Inner Realms have been Aspects of Zertihn, in one way or other.
( a character that has followed Zertihn will therefore "break loose", some way or other in their divine march towards divinity, defining their own uniqe aproach to things ).
4.
Age is indeed not a matter in the Inner Realms but most commoners actually live governed by the rules of any other primeplane experiencing sickness age etc. They do this becourse this is how they collectively experiences and understands the world and as such the Inner Realms abides to their needs and believes. It is commonly known amongst commoners that many adventurers do not seem to age and holds or aquire powers allmost unimaginable, but they are "used to this" and merely refers to these as the "Reborns" or the "Prospects", being those most likely to eventually become Reborns.
Allthough age ultimately is unconsciously defined by the soul itself noone is capeable of actually becoming younger without the direct intereference of the Inner Realms or Zertihn himself.
5.
As mentioned ealier Zertihn was the only actual Diety in the former incarnation of the Inner Realms. In all other planes in the known multiverse this too is the case that only a single diety or a colaboration of likeminded dieties calls a given plane their home and can actually enter it and function there. Thus in the seven heavens even if a follower of a evil God managed to gain entry it would be unable to communicate with its God and the God would loose all communication and knowledge of what was going on there.
As the Inner Realms is also the centre of Hope and seen from a divine perspective Zertihn wish to learn he has uniqely allowed other dieties to "function there by proxy". What this means is that no other gods have actual access there ( unless invited ) but their can communicate freely with their followers there. Zertihn is completely omniscent so whatever transpires between the Gods and their followers is know to him in his aspect of HOPE and aspects of "AO". When dealin with his own portefolio's as diety he is utterly clueless to these things unless informed in more traditional ways. The reason for this selfrestrictment is that he fully realises he would tamper with his own portefolio and personal lerning experience if he had such knowledge available. Thus is is fully possible to fool Zertihn the God of just rulership, culture and civilisation but the instant these things tampers with the Inner Realms, HOPE or inhabitants all is revealed ( and allways were ). Allthough unconfirmed rumors have it that the more furious aspects fo Zertihn both from his lineage as dragon but also as "Initiate of Pain" will enact furious vengeance upon and and all daring to interfeer with the free will and freedom of any souls taking refuge in the Inner Realms. This has also gained him some notions of respect from the more dark side of the multiverse seing that he fiercely defends also their followers right to strife for their hope !