You say you grabbed a judo point and shot that. Then you mentioned you shoot VPA SGT heads. Forgive me, but did you hit the squirrel with the judo or the VPA?
If you shot him with the judo and he still ran up a tree, I've had the same thing happen before. I quit using judos on squirrels. Quite a few guys use old broadheads if they're on the ground since they are such tough skinned critters. But I wouldn't suggest that if they're up a tree.
If you shot that squirrel with a VPA SGT and hit him square in the chest, he should have been dead. Them things really pack a punch.