I assume, then, that you have very little to no character turnover during the campaign? Permanent deaths? Retirements? Players dropping out and-or joining up?
At 1st or 2nd level (I can't remember exactly now) one of the PCs died - the wizard initiate of the Raven Queen. I asked the player if he wanted to bring in a new character or keep going with that one. He wanted to keep going, and suggested that he might be sent back to the world on an important mission. So I narrated his spirit's encounter with the Raven Queen in Letherna, and the intervention of Erathis, who asked that he be sent back to the mortal world to recover a sceptre hidden in the Nerathi ruins where he had fallen in combat. Which duly happened. (Mechanically, it was adjudicated as Raise Dead, including an appropriate deduction from the treasure parcels for that level.) That sceptre turned out to be the first recovered piece of the Rod of 7 Parts.
The same character died again at 15th level. When the PCs had him resurrected, he was sent back to the world in his fully reborn form, as a deva invoker. (The player wanted to rebuild his PC, based on changes and developments that had occurred during play.)
Full story here.
At 3rd level there was a "TPK" - one of the PCs, the paladin of the Raven Queen, actually died (to friendly fire), while the others were knocked below 0 hp by undead under the command of a goblin shaman. I asked the players who wanted to keep going with an existing PC, and who wanted to change. Only one wanted to change. So 3 of the PCs recover consciousness in the goblin cells, with a new cellmate (the new PC). They can smell the roasting flesh of the half-elf (the PC abandoned by its player, now being cooked by the goblins). The body of the dead paladin, meanwhile, was laid out on an altar by the goblin shaman, who was using the paladin as a channel to summon the spirit of the paladin's dead nemesis, in the form of a wraith. The summoning was successful (by way of GM fiat), but the paladin was also sent back by the Raven Queen to stop the summoned spirit going wild in the world. Which he and his friends, in due course, did. (Mechanically this was also handled as Raise Dead, as above.)
The only other deaths were fairly recently, around 24th level or so. Two PCs - the fighter and the paladin - died in a difficult fight against starspawn carrying the true name of the Raven Queen, and the angels of Vecna who were trying to learn said name. The other PCs, after defeating the final enemies, took their bodies back to a friendly homestead in the area that they had last visited around 20 levels ago, and stayed there for a day or two while the invoker/wizard Raised the dead PCs.
(I'm not counting the half-dozen or so "deaths" that have been immediately countered by "once per day when you die" effects that are pretty typical for epic characters. The paladin has two of them, the fighter, ranger-cleric and invoker/wizard one each, and I think the drow sorcerer might have one too.)
Because if you do have such turnover, the very existence of the heretofore non-party-member replacement characters makes it pretty obvious there *are* other adventurers out there; as the replacements are getting their levels and loot from somewhere.
If a new PC were to be introduced at this point in the game, s/he wouldn't be an "adventurer" who had acquired loot from random tombs. (That's not where most of the PCs' equipment came from either; it is mostly bestowed upon them as blessings from the various gods they serve.)
Depending on details, of course, s/he would most likely be the exarch of some god or other power sent to work with the party in this hour of cosmological crisis!
