Hey there matterhan,
First thing...take a deep breath....
I'm assuming the temps will be cool enough to let him lay overnight. Let's assume he's hit a bit far back. He should bed down very close to where you last saw him.
It will be a long night for you, but I STRONGLY suggest you don't go back tonight. If he's gut shot, that will do nothing but push him.
Hopefully, he shouldn't be far from where you last saw him.
Please keep us posted. Be sure to reply and let us all know how it turns out.
Regardless of what you find at first light tomorrow, spend as much of the day loooking for him.
Good luck!! I'll toss a prayer up for ya!
Paul K. "aim small, miss small"