Frankly, my real opinion is they shouldn't get any kind of a victory. The one who fled should take a loss, but the other one did not get a real win at all.
Some people flee when you have cast the kill spell but before it actually kills. Can't penalise the attacker for this. Penalise the person who flees. Currently they miss a few arena tickets and can't join PvP for 5 minutes, which isn't much disincentive. If you start reducing benefit to winner, more losers will flee to spite them. Besides, if someone flees in tournament you do still get 100 points - it is only 90 for a bye.