This happened to me last year on my first elk hunt. Shot a bull in CO and he folded up like a lawn chair and rolled down the mountain a few times. I pack up and hike down my ridge and back up the far ridge and when I get up to him he gets up and ran off. Decent blood where he was laying but nothing in the snow he ran through and enough tracks from the herd that tracking a single elk wasn't happening. I looked high and low all that day and much of the next. No sign or birds anywhere. Pretty dejecting feeling still a year later.