Here's my take...
#1...no its not as decay resistant as the heartwood,but if the woods properly harvested n stored,and then made into a well made bow and taken care of right itll last a long time and outlast you...
#2. I've seen enough examples that yes it can...(although I've never done it)
#3. Yes it does bend well to heat..but not as good as osage IMO...
#4. I've found the low elevation n density yew to benefit from a light tempering...just don't overdo it,and make sure the heat doesn't wrap around n scorch the sapwood as it won't like that at all....