I would hazard a guess and say respawing dungeons will not be a thing (just like metal nodes not respawning) because this would be counter to the idea that the player needs to keep exploring and pushing ever deeper into unknown territory to progress.

If dungeons respawned (take for example a Burial Crypt you found a core in) then there would really be no reason to strike out and find more crypts - just wait for the crypt you found to respawn, clear, loot and repeat.

In essence you would only need to find one dungeon that held an item you needed in each biome and merely farm the respawns never having to risk exploring and finding more.

Just my take on the matter.

If you enter the 'devcommands' and 'debugmode' (need to add '-console' in your properties under launch options first). Try typing resetspawn near the location.

The only thing I'd care about having respawn in dungeons are the seeker larvae, but you can farm them at the Mistlands boss too.

The Ghost enemy doesn't drop a trophy or anything else, and all the other "rare drops" from enemies found in dungeons can be found in the overworld as well. Cultists and ulv both seem to have 10% drop chance for their trophy, and rancid remains makes a frequent appearance in skeleton surprise events. Draugr elite trophy can be farmed outside.

body piles in the swamp will spawn back after a short wile but dungeons will not :)

Mod tweak that allows this though....

Its not, and i don't think it ever will be.