Your deer will heal in about one week - if I had to guess. Its odd that you never found the back 1/2 of the arrow. I'd guess the arrow ran up the shoulderblade or even higher towrds the spine without penetrating the lung cavity.

You did an excellent job of tracking. Knowing that you hit high in the front of the deer - He will almost definitely live - considering how for and long you tracked the deer. Imagine w/o snow how hard it would have been.

Its tough to learn from a mistake, when you cannot know what exactly went wrong. I'm sure you've surmised by now that they do not usually go a fraction of this distance with a lethal hit from an arrow. Alls you can do is to know that you did your best, and feel confident that you honored the animal with a dedicated follow up. My hat's off to you for your effort.

Now, shake it off, and hunt well.