Allright.. So we've run into a bug where it is no longer possible to unretire previous adventurers in the current, and recent, savegames. I've been messing with the save, there might be a way to salvage one or two adventurers, but it will be a glorious mess.
I've managed to track down most if not all of our retired characters. I've indicated their positions on Timeless Bobs map of dinerwandered:
Yes, that's correct, everybody except for Mrwillsauce and Eric Blanks character are squatting the same house just west of King's Boulevard. That's three or four necromancers, a vampire, their companions including goblins, a number of zombies, and several innocent people. Our local eerie mist thrall might also be among the inhabitants, I didn't check. The moment anybody enters the house or gets near it, all hell will break loose, and all our great heroes will start bashing each others brains until only one is left standing, and some will drop dead due to old age. (I must admit that this is an absolutely epic fight to watch..)
Now even with all those adventurers dead, the bug remains.
However, I think that with dfhack, it would be possible to build a fortress on the site and switch control to a selected adventurer (edit: another method has been found, you can travel to the site with another adventurer, then switch control to the character you want to unretire). If the 'unretired' adventurer survives the mother of all DF battles, he could then continue on his adventure, but most likely all others in the "adventurer home" will kill each other, so there will be a lot of collateral damage. This needs some further testing (I won't have time to test this in the next few days though). The good news is that with Mrwillsauce and Eric living at the other end of town, Kromgar's character is the only one in that house who is still on the play list, so others might be expendable.
Edit: so the only way to work around this bug might be to hold a massive fight-to-the-death between all our adventurers. DF is the most glorious game ever.