I don't see any logic behind a person purposefully logging off the server in the arena other than to escape death. Most people can wait the ten seconds of /leave.
I'm also worried that this will be the newest way to pvp log because not only does logging out keep you from dying, but it also gets you out of the arena. People can pull the, "oh I was lagging, but now I'm not in the arena" card.
Not mention, I often lag in pvp and the only way to stop the lag is to relog. I'd rather not be tp'd to spawn when I relog in pvp for a good reason and I'm not in combat.
I'm no mod, but I think that the current pvp logging rules should stick, and if a person chooses to log out for a long time in the arena, they should face the consequences.