WOW!
Well good luck on him. It's hard to say what happened exactly. Maybe you will get him and be able to find out.
The one thing I have learned over the years, deer are very tough and resilient animals. Sometimes they amaze me.
My 11yr old nephewshot a doe last weekend with a m/l, 15yds broadside. The shot nicked the back of the shoulder and blew a hole right in the heart. The deer traveled 150yds, bleeding like crazy...and when my bro-in-law and nephew got to her, she was still alive and kicking. Amazing, and with a hole in the heart to boot. I always expect the unexpected. Good luck.