I've read from someone in a topic somewhere on this forum that if you do not pick up the loot from dead enemies that the map will not spawn new enemies. That's cool for New Sorpigal as I'd prefer it as part of the storyline, but in places like Mire of the Damned, it'd be a welcome mechanic. The only way I see of screwing it up is when the enemy flees to outside the borders of the map and you shoot them dead without being able to loot them, as you're redirected to the travel screen. This issue just arose as I cleared New Sorpigal and noticed I can't claim one goblin's corpse. Again, for New Sorpigal, I don't mind it, but on other maps I'd enjoy fighting certain enemies again. So, I think if I were to leave the map and return, those fleeing enemies might return to their original locations within the borders of the map, I'm hoping at least.

I am not sure where did you read that, but that information is totally wrong.

Everything on the map will respawn on the timer, which starts from your first visit to the zone.

Sarisio is correct. I would add that the timer is quite long in in-game time, something like 6 months I think, although it varies per zone. When I played, without trying to optimize or powergame too much, I only encountered a few areas that had respawned, and they were obviously the ones I visited in the early stages of the game so it was no problem to clear them again with my much more powerful party. If you are specifically hoping to tackle enemy mobs again, you'll have to spend a lot of in-game time waiting for respawns.

New Sop was every 6 months.
The first respawning was always useful because of the expensive books still to be bought around that time.

Just a tip, but don't forget Telekinesis. It works to grab those bodies that are out of range. Or activate a switch that's in sight but out of reach. Rather nice to be further away when chests explode, too.

Or when you'd rather avoid having to fight everything between you and the treasure chests or some other item laying about. Don't bother running all the way to it, just use Telekinesis to open a chest or pick up loose items from a further distance. Very nifty when set to the quickspell. Then run off. Or equip whatever would help to eliminate what was guarding it, and fight them with their own treasure! Ha ha!

I've yet to figure out the range for Telekinesis. The Ur-Mage Klavis Verge said (in the manual) that the skill in Mind Magic affects distance and strength.

As for respawns, they sometimes happen quite often. The Hive respawns once a week. Typical times for outdoor maps are every three months, or six months, or a year. You'll notice if you keep a journal.

If my notes are correct the map respawn rate should be something like this:

6 months - New Sorpigal, Mire of the Damned, Dragonsands, Hermit's Isle, Paradise Valley
8 months - Bootleg Bay, Eel Infested Waters, Kriegspire, Sweet Water
2 years - Castle Ironfist, Misty Islands, Silver Cove, Free Haven, Blackshire, Frozen Highlands

7 days for The Hive should be correct, also as mentioned before, not looting a corpse should not prevent a map reset iirc. Telekenesis is certainly the way to go if a corpse, or the chest in Paradise Valley is beyond the map boundary.