Seems to me that it should be on a case by case basis. Certain low-level offenders could be "paroled" after a certain period of time with the caveat that a subsequent offense would lead to permanent banishment. Other offenders, like those who shut down The Cage for three days with computer-generated spam :Ahem:, should be given the equivalent of "The Death Penalty," i.e. a permanent, lifetime, irrevocable, non-appealable ban. It depends on what they've done.