Hendryk

Then make it a fraternal twin, born at the same time as the PC but shunted aside by Mom because the "lesser" twin was born without the Bhaal taint.  The midwife, prompted by whatever vision you please, took the lesser twin away instead of killing it and... (backstory) to a time 15 minutes after the end of ToB when the original PC ascends and the cosmic connection kicks in.

Seems to me that there would still be a problem in concocting one single story that would be appropriate to all PC classes and alignments.  It would smell really cheesy to give, say, both a paladin and an assassin exactly the same upbringing; much too much like Candlekeep, however it's handled.  Simpler, perhaps, to fudge up some story about a "chosen" child, born at the instant CHARNAME ascended and mystically linked somehow to the new god(dess).  

For baddies, perhaps an unrepentant cult of Bhaal worshippers?  They know about the new PC's connection to CHARNAME (old PC) and want to sacrifice the new PC in a ritual attempt to force CHARNAME to assuming Bhaal's old portfolio of murder whether (s)he would or no.  Meanwhile, regardless of CHARNAME's class or alignment, these cultist have been worshipping him/her as the God of Murder with some success.  Note, too, that the sacrifice idea would prevent even an Evil PC from cooperating with the cult which would eliminate alternate story lines as in the "champion" idea.

The nice thing about the idea, though, is that it would allow cameos, based on their epilogues, for current NPCs some twenty years later.  Most of them wouldn't be easy to find and none of them - except Minsc and Jan, maybe - would be willing to talk to you without your doing them some little "favor" or other.  Side quests then would be there in profusion.

Different strokes, I guess.  You seem to want something like a Greek tragedy out of it while I'm all for a light comedy of manners.  

Oh well.  I'll be good and shut up now.

And a part of the fun of a post-ToB mod would watching NPCs, who formerly adopted a very haughty or bullying attitude, cringe and crawl before the mighty PC.  And if the PC were fool enough to leave bodies lying all around Athkatla as in SoA, (s)he would discover that *now* his/her every move is noticed by everyone and all deaths have to be accounted for in the courts.

Sure.  The PC, at the player's option, could simply respond by going on a rampage and killing everyone.  That would attract the attention of Elminster, Khelben, et. al. and END GAME, no matter how tough the PC was.  As for free play, having such an uber character try to "fit in" somewhere in society would do for me.  Otherwise, it would be just another middling character with a lot of angst and guilt to work off.  I get plenty of those in RL; don't need to roleplay for 'em.

Note that a new romance, with a relatively very low-level NPC, one who would definitely be challenged going one-on-one with an ogre, would be a nice way to rein the PC in - if the NPC were attractive and amusing enough.

I love the idea of post-ToB adventuring and the tools now are vastly better for the job than when Silverose first proposed the idea.  However, I think the RP aspect would be greatly diminished if the PC were reduced to a 5th level nobody.  And all your companions dead?  Even if they survived the Throne in fact?  That's putting a terrible strain in *my* sense of continuity at least.  If nothing else, this 5th level shlub would have all this god-like equipment plus the stats from all the tomes and the machine of Lum the Mad.

I'd much prefer an adventure for high level characters.  It would be simple enough to make much of it a matter of RP wherein the party's levels were irrelevant.  For the main combat, create a challenge area that is chock full of fairly difficult encounters, that spoils potions and scrolls and allows no rest.  If Amn were chosen as the venue, for example, the mod could mostly involve politics at the very highest level and ultimately a confrontation with the Twisted Rune.  Not in that silly single room off the Bridge District either but a properly complex and defended lair, suitable for one or more of the most powerful and ambitious liches extant.  And if you don't want the Soa/ToB NPCs, they almost all have business of their own to tend to after ToB.  Let them make their farewells properly rather than snuff them so off-handedly.  Some might even recur for cameos as the non-party NPCs from BG1 did.