MikeWorks is a good example of redemption. His initial reign as a mod was before my time, but from what I gather, he was kind of immature and bothersome at the time. However, he did eventually grow out of that phase. Would his old persona be permabanned if he posted like that today? I don't know, but if he were then we would have missed out on a good poster a few years down the road.
In my opinion, life sentences can be easily be warranted in society when involving convictions of murder, rape etc. but to never be given another chance on an online forum, a poster would need to do something extremely heinous to justify that sentence.