Dragonball (and most of the other festival PvP games) needs dishonor like GW1 had. Today, 20 points. At 20 points down, someone left. 40-20. Then, they showed back up again. Meanwhile, our team lost a few more kills, so he left again.
This is ridiculous, but what's even worse is the solution. When someone leaves like that, it leaves his team short a player. If nobody else joins, quickly enough, then more will leave. THEN, the other team -- yeah, the better team -- has to give up a player to the weak team.
It's just not fair.
If someone leaves, FOR ANY REASON, they should be preventing from playing for at least 15 minutes. And, if they do it again, make it a day. Or more.