If the deer was quartering away and the arrow hit directly behind the front leg it hit vitals (heart/lung). I would bet that you didn't find blood because there isn't an exit wound and the arrow is plugging the entrance. I shot a buck a couple of years ago like this. There was only a drop of blood for 300yds. Fortunately I was using the game tracker string at that time and I was able to follow it straight to the deer. I would bet that your buddy's deer is dead. Sorry you couldn't find it.