RE: Deer hit, tracking suggestions.
Not that it would really help now, but here in NY the state authorizes a special service that uses dogs to track deer in cases like you've found yourself. Not sure where you are, or what the laws are, but I would imagine that if you had a dog on a leash and no weapons on you, the dog could probably track it.
Don't beat yourself up too bad over it, it has or will happen to everyone. Fling a few arrows at the 3D target so you know your sights are still on then get back out there.