Don't beat yourself up too bad over it. (easy for me to say huh?). That's the sick thing about bowhunting that we've all experienced at least once in our lives. 2 indifferent hits in 15 years is pretty darn good. Good chance it is still a fatal hit. There are many arteries in the neck. Good choice in backing out and waiting for him to expire too. Good luck tracking him.. let us know how it turns out. Keep an eye out for your arrow too.