The Last Word

Two thoughts on that.

First, Tenebrous comes back after having used the Last Word a bunch, so it didn't destroy him, though it split off his divine essence, which suggests it can be resisted to a point.

More importantly though, the Last Word is what is supposed to destroy the multiverse eventually. If it is to destroy the multiverse, that kind of implies that it is irreversible. So, I think for a god to be brought back after having been subjected to the Last Word requires throwing the concept behind it out the window. If the Last Word doesn't irrevocably destroy things, it sort of ruins its mystique. It's very name is meant to imply finality, so if you start bringing God's back, its almost like a cheesy twist ending. It's telling a story only to undo the central point for the sake of a cheap narrative trick.

That being said, if really want to bring a God back that was destroyed by the Last Word, my suggestion would be to say the God was never destroyed in the first place rather than having them come back. Possible explanations for that are that Tenebrous was not destined to wield the Last Word, and thus it did not achieve full effect. Or perhaps some Gods used various forms of trickery to make Tenebrous think he had killed them with the Last Word (celestial Body Doubles anyone?) and went in to hiding until he stopped being able to use it. Maybe one god knew some other similar True Word that counteracted or mitigated the effects of the Last Word.

Personally, part of me thinks the whole True Word business is a bit silly, sort of like Wishes for Gods. It takes a fairly ridiculous notion (the ability to reshape reality without creative effort) and makes it so Xtreme, only a Diety can use it! But there is something the True Words represent that I think has its appeal. D&D is notorious for power creep, and stories about Gods just take it to the next level. True Words are interesting in that there is a finality about them. There really is nothing more powerful out there. if you are going to be using such narrative devices, I don't think I would go about undermining their relevance. The idea of True Words suggests there is some inherent underlying rules that shape the multiverse. If you just counteract it by saying there are loopholes and More Powerful Stuff, you just restart the narrative arms race that True Words are meant to end.