This isn't allowed?
That is just an duel. If the person is bored/tired bla bla bla of any duel, he may quick it.
Sorry Freak, but it is not allowed. As Quickplay said, if you really have to go, you should let them kill you, it's just a game. Another time the other guy will have to quit, and how annoying would be if you chased him and he just left? Of course, real life is more important than playing, sometimes we have to quit IMMEDIATELY, such things happen, rarely, but still. And that's why admins warn people before punishing them hardly. If someone leaves a duel once, I would warn him, even if he claims he had a reason. If he does it again, finding another reason, I would either punish him slightly, by killing or something, and warn for the last time, either just warn, if I believed him. But if it "accidentally" happens to him for the third time, I would punish him a little harder. Finally, if he continues doing so, every such abuse is a step closer to a ban.
And if anyone says there is no such rule that disallows using /class to avoid death, well...
Common Sense
First and foremost, common sense should be used at all times on littlewhitey's SA-MP Server. If you know, believe or even have a suspicion something you are doing is wrong and could get you punished then you should not be doing it - if in doubt, contact a member of the team for more information.
The command was designed to safe people from the neccessy of death when they just want to change skill. Using it in any other purpose is an abuse. There were discussions about removing/changing it, but developers got to a conclusion that players are trustworthy enough to be given such advantage, no need to punish those, who use it in a right way.
If a person is bored with a duel, it's his problem. Noone forced him to accept it.