I agree that it depends on the situation. If you know the deer will be down by the time you can even get to the ground, then go for it and track it. That can be hard to decide, because I've shot deer that I was sure I double lunged, but I only got one lung and they made it a couple of hours, making for a pretty rough tracking job. Overall, I think losing the blood trail isn't nearly as bad as bumping the deer. I've tracked a lot of deer that left little to no blood trail. It makes for hard tracking, and youre more or less searching than tracking, but it can be done. I would let the deer be, and risk losing the blood trail. Its better than losing the deer if you bump it, and if it's down, it can be found with a thorough search. Dogs help too. Even a dog thats not trained to find deer can run across it. Ive done that as well.
I think when you weigh the pros and cons of this situation, and consider the ultimate goal is to find the deer, it becomes an easier decision to risk losing the blood. A blood trail is by far the easiest way to find the deer, but its only one way, and it can be unreliable. Blood trails mysteriously vanish all the time, even on a well hit deer. You could get to tracking before the rain comes, and the trail disappears anyway. In the mean time you bumped the deer and now its 500 yards farther down the trail. A blood trail is only one method of recovering a deer, and I think if the situation says let the deer lay, then the deer should be left to lay no matter what that means for the blood trail. Blood trails arent the magic bullet we can't live without, it just makes us use our other skills if we lose it.