I've sent a bug report in on it.
Essentially, with the Crimson Dragon invasions, Tomas got "un-stuck" (he was in a fixed position), and unlike the other Collector Quest NPCs, he COULD be turned Cowardice or Hatred.
If Hatred, he would chase people (and some people found they could actually exploit that to use for nefarious purposes, as certain skills could target him once outside city limits, even if he couldn't die when back yellow).
As the Trinsic infection area extended from the swamp to the south, to the river to the west, and north to the edge of the swamp between Trinsic & Britain, he could have chased people ANYWHERE in that area.
Worse, he will, even now, chase hostile monsters and kill them, which can lead him slowly even FURTHER from town.
I found Lake Austin's Tomas two screens north and west of the NORTH EXTERIOR CORNER of Trinsic (the wall outside the moat). Once I saw that he would get medieval on anything hostile, I found a nearby ogre, had the ogre chase me by him, then HE chased the ogre. I walked to Trinsic, healing as I went, and let Tomas kill the ogre inside the city walls. Once there, he started wandering around town (last I saw, he was walking on water south of the meeting hall).
I'm sure similar strategies could get him back into town, on the other shards. The hard part will be to FIND where he ran off to in the first place. But that's only a partial fix - the devs need to have the GMs put him back into his static position.
