It's funny -- I find myself agreeing with both sides here. On the one hand I am one of those that hates the dead, empty feeling of a world where enemies never respawn; but I am also very easily irritated by having to wade through battle after battle just to get somewhere.
I would be very pleased with a happy medium scenario -- maybe very slow/limited respawns. If you kill all the bears you can find, that shouldn't lead to the end of bears in that world. Maybe the bear population stays dead for, say, an in-game week, and the slowly starts to rise again, perhaps capping at a lower point than what it started with so you don't run into that scenario where everything is like you were never there.
If they won't put that in as a part of the base game (and it sounds like they won't) then hopefully we can use the editor to make some enemy respawning mods, as dwelfusius mentioned.