I don't know. I don't think enemies in caves/dungeons will respawn; they typically haven't in any past TES games. Respawning is possible, the engine allows it, but I don't see it happening in Skyrim. It'll probably lock like everyone thinks it will -- with a slight chance of weaker/tougher foes. Just a personal opinion though; anything's possible.
Actually, enemies in dungeons did respawn in past games. In Morrowind, bandits and other humanoid enemies generally did not as they were unique, hand-placed NPCs (Unique in the sense that they were placed in the world and given names, as opposed to generic enemies that are just spawned based on a leveled list, not in the sense that there's anything actually setting them apart from other NPCs as characters.) Monsters, however, usually did respawn unless they were unique ones. And in Oblivion, leveled enemies would typcally respawn, including generic bandits. I'm guessing this will remain true in Skyrim as well.
Regardless, though, I'd say level locked dungeons are an improvement over Oblivion's level scaling as part of the problem with it was that enemies always got stronger as you leveled up, making gaining levels seem a little pointless, with level locked dungeons, if you go into a dungeon and find the enemies too powerful, you can leave, go gain a few more levels, and come back, allowing you to defeat the enemies there more easily, because you are now stronger than when you first entered the dungeon but the enemies are not.