My thoughts are simple: if you punish a person for leaving, you might be doing it unfairly, since the reason might be plausible. If you don't, you're making another user upset because they lost their replay and their win.

A solution is hard to come up with, because it's a turn-based game. But still, I think the spec/quit = loss solution could be applied. Look at the turn-based strategy games all around. When you leave mid-game during a game of that kind, it counts as a loss, considering you're 1 on 1.

From my personal experience, I haven't had many people quitting on me, to be honest, but that's because I choose who I play with very carefully. You regular players might not have the same nitpicking habit as me.