to answer yer question.....in my experience once you pass 300 yards yer odds go down on finding that deer, and certainly after 500 yards the odds drop a LOT.

I have tracked a few deer over 500 and found them with a dog. A deer that can go 500+ isn't hit well at all and may not be recoverable...but as long as you have blood I'd keep tracking. Might be able to bay the deer and kill it. I tracked a buck prolly 600 yards before dog bayed a very much alive buck that decided to fight instead of run. It got ugly fast but the deer was shot again and dropped. It had been shot four times by the original hunter, but not in a fatal spot.