I'm curious, too, how the bunny died, since there's allegedly nothing wrong with bunnies living outside in any temperature extremes (according to some breeders).
My Dad is a breeder, and you don't really have to worry about cold weather, during the winter we put a tarp around the pens to keep out wind and rain. But extreme heat is totally different. Rabbits get heat stroke easily, so when you have outdoor rabbits in extreme heat you have to be really careful. I know my dad has lost one or two rabbits due to heat stroke.