Is there a finite amount of foxes/wolves/horkers, etc.?

Since the corpses of all the wild animals I kill seem to exist in the world forever, I can't help wonder if there is limited supply of these creatures. If not, how long before new ones are created? And will the dead animal bodies ever decompose?

I am not positive about this; some of the information with regards to respawn timings are a bit weird at the moment. From what I can tell it's around 15 in game days for respawn. I'm not sure if this is exact; it might be dependent on you not visiting the area for a certain amount of time, but I don't think this is the case. Also for corpses to decompose I believe it is about the same time.

Edit
I believe it actually takes longer for bodies to decompose then it does for creatures to respawn as I had killed a guard in game and the guard respawned but his old body was still there. It might even be that visiting an area stops the decomposing of body but not the respawning. I will do some more tests soon =)

There are an infinite number of animals to whimsically slaughter as you see fit. The corpses you've strewn across the land will eventually despawn, but in the meantime the game is perfectly happy to spawn new innocent, unsuspecting, fuzzy little targets for your depredations.