I didn't even bother to read through all the animals' characteristics and loot, because that's imaginably subject to change majorly.
However, supergrid-wide rare animals? FUCK YES. As for week-long spawns... Maybe a day-long respawn timer is enough, considering the difficulty of searching an ENTIRE SUPERGRID for ONE animal. Consider a few things; One, the size of a supergrid. How long would it take to systematically scan through everything? Imagine with the default client as well. Two, the difficulty of navigating a supergrid. Unless you have insane con and can cross rivers without a boat, you're going to either crawl around carrying a boat, or spend 10 minutes building a boat everytime you get to a river. Three, animals can hide behind trees... 'Nuff said. I do understand the concept of rarity, but week-long respawns might be overdoing it (what with server crashes and all?)
On the note of server crashes, their corpses should be semi-permanent in case of server crash; especially when waiting for your village survivalist to log on to skin it without wasting quality.