Last year my partner shot his bull right at dark in Sept. We thought it was a good hit but accidentally snuck up on the still alive bull in the dark. We didn't want to risk bumping the bull and losing him so we backed out and came back and found him at first light. Broke him down and packed him out without losing a lb of meat.
Mike
I had the same happen two years ago with an archery bull. He only went about 75 yards after the shot and laid down. I watched him until it was almost dark, he knew I was there but didn't get up and run, which I took as a good sign. He was trying to hold his head up, but having a hard time of it. Right before dark his head tilted over and he laid it on the ground. I thought he was out so I took one step toward him and he got up and trotted off into some very thick oak brush. So thick that no amount of light would help.
We came back the next morning at first light and found him right off. So did a big black bear, he'd just gotten to the elk when we did; chewed the Colorado-required evidence of sex right off the carcass but that's all he ate. We got right to work and boned out the meat using he gutless method, and didn't lose any. The pack out was a short one and the meat went right on ice. If we hadn't found him right at first light, I'm not sure the maet would've been good.
I also recovered a cow several years ago at first light during September and lost no meat. I'd shot her right before dark the evening before; she ran first one way, disappeared over a knoll and then (I found out later) did a 180 out of my line of sight and went the other way. She ran a total of 200 yards and piled up, with a ,50 caliber bullet hole through both lungs and one clavicle. Anyway, I looked for her for 3 hours, had a good headlamp and all but I was just looking in the wrong place, in the direction I'ds een her run. There was no blood trail, and she'd run through an open meadow with elk tracks everywhere so there was no trail I could follow. Especially since I was looking in the wrong direction. Came back at first light, heard a bunch of jays and magpies causing a ruckus, and found her straight off. I was seriously pissed at myself for wasting the meat, because I assumed it was no good. I couldn't even think straight. But my partner said "lets make sure it's no good before we write it off," so I skinned and filleted out a backstrap and it was fine, as was the rest of it.
So, I wouldn't leave one overnight on purpose (I have my best luck in the evening and have staggered back into camp around midnight a few times) but if it happens, I won't give up on the meat, and I'll try to be there right at first light.