Yes I believe the Lurkers re-spawn or there's more than one per dungeon. I've fought 2 in the same dungeon on the same playthrough but in 2 different visits. I believe there's a away to check how many Lurkers you've defeated in the dungeon as well.
And no the status of the dungeon resets on a new game. Whatever treasures you've collected will be in the dungeon again on another playthrough.









