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.