Since conceptionally the stuff that happened in the final 2e module Die Vecna Die were in the past, I have a revisionist version of that as the backstory.
Basically it goes that the adventuring party that put an end to Vecna's scheme were Tarsheva Longreach, Akin the Friendly Fiend, Fell the Fallen Dabus, Kylie the Tout, Prisine the puppetmaster of the Will of One, and Lissandra the Gate-Seeker. They travelled through Oerth, Ravenloft and Sigil and kicked Vecna around. Rather than having the Lady of Pain ask them to do something, they instead picked up on the signs of what was happening and acted all on their own. They rallied a small army of concerned Sigilians, stormed the armory and defeated Vecna and his minions in battle.
They were rewarded with something from the Lady in the end rather it be a secret, a pact or a gaurantee, for knowing and doing what she wanted done, without her intervening too much (which would have drastically effected the multiverse, the more she did about the whole thing). In many cases the reward they got from the Lady was that they wouldn't get mazed or flayed for some of the things they've been doing. For others it was a simple matter of immortality as long they were careful about their actions.
All members of this group have a connection to Ely Cromlich, in that he is their arch-nemesis, however they know he's the one with the key to killing Vecna once and for all. Currently they know he's out there with a grudge against them all, but at least a few of them are planning on manipulating Ely for one of their schemes.
Our Lady's Ward Chantcaster
Third Week of Sacriligion
(Thames Brobank, culler)
LICH-GOD TRAPPED IN ARMORY
Tragedy struck Our Lady's Ward last night as a lich-god from the Prime found itself trapped in Sigil.
"The poor thing," sympathized Terrycoat Spectus, noted Seeker factotum and still avid devotee of the Source. "It must have been in the middle of ascendence into a higher state of divinity when it wandered through a portal. With its godhead in a state of flux, the Lady must not have cared enough to warn it away. The pain of existing as a power in Sigil must be overwhelming."
Theologists such as Doctor Horatio Milton of the Street of Clandestine Affairs surmise that the creature was in a state of confusion when it first entered the City of Doors.
"Powers who transmogrify themselves into more intense divine states often spend years, decades, even entire cycles cocooning themselves in their realms while they adjust themselves to their increased power and responsibility," he said. "Of course, evil gods are often especially confused as their additional power necessitates a whole new level of corruption they weren't previously aware was possible."
Consultation with the theopaedias in the Street of the Gods' Hall of Registry identified this particular lich-god as Vecna, known on his home world as "the Whispered One." This, according to Milton, explains a lot.
"Vecna spent centuries in a tower previously occupied by the Doomguard," he told us. "As bewildered as he must have been by his new environment, he would have gone immediately toward the Armory's familiar smell." The combination of negative energy and intense entropic activity, explained Milton, as well as the body odor left by some of the faction's older members before they were disintegrated, produced a very home-like environment for the frightened Power.
According to the reports of Lawrence Kane of the Planes-Militant, the arch-lich has spent his time "Not doing much, really, just raising hordes of unliving minions, blighting the area with horrific banes, and whimpering occasionally. My men can handle it."
"He's too confused to find his own way out of the Cage," Dr. Milton concluded. "The pain must be getting worse and worse all the time. For compassion's sake, we should do something to help him."
Eight former Dustmen have attempted to lure the god out with a sack of larvae, to no avail.