yup, sugar maple I've heard makes a fine selfbow. I guess if it simply fell over the wood'll still be fine after a few months, it fell during the winter so the tree was "hibernating", and probably didn't realize it was dead until you cut it
. Cut some Black Locust last month that had been pushed over by Sandy and the sapwood was in as good condition as if they had still been standing.
Whitewoods will rot quickly if they are cut and left outside, so if you want to get more maple you'd better do it now. If it were me I'd split it, debark it, seal the ends, and let it dry. You could cut backing strips too I suppose, it's your wood.