I don't think there's a single answer to the question "What should be done about powerful characters". There will ALWAYS be characters that seem overpowered, for one reason or another, and in many cases they're good for the game.

I'll digress with a quick anecdote. Way back in the day, I was pals with the guy who played Gareth (though I haven't talked to him in years now). One weekend a few of us were staying with him in his dorm room in Minneapolis for the weekend, in January. Now, there isn't much to do in Minneapolis in January that doesn't involve freezing to death, so naturally we planned on staying in and playing CF. Woe is us, however: CF goes down for like a week straight, starting right then. So instead we hatch this plan to go kill things on a wimpy CF clone mud that shall remain nameless. We know nothing about this mud, except that it started out as a CF clone and evolved to its current point. We roll up three characters, follow Gareth, and he proceeds to take us on a slaughter of everyone in the game until the imms ban us.

The moral of this little story? We gave Gareth a completely different environment, with new skills, classes, races, areas and players, then set him loose and he was an instant killing machine. (He's by no means the only player like this.) Overpowered combos aren't a problem until they end up in the hands of a player who can fully utilize it.

But there's more: people can tolerate overpowered combos in the hands of extremely skilled players. It's all in how the aforementioned player uses it. A lot of characters that rack up tons of kills, also take lots of risks to do it. This seems particularly true with warriors, who can roll with hundreds of kills but also forty or fifty deaths. To use Istendil as an example, he was hugely powerful, but (it seemed to me like) he took lots of risks with that power, including anathing himself and taking on pretty much everyone. Of course he hardly ever died, but he definitely took chances.

These sorts of really powerful characters played by really skilled players are iconic, and a huge part of what makes the game fun. These are the characters we all talk about years later.

The thing that really seems to put a damper on it all is when a number of things converge. For example, a skilled player gets a very powerful combo, then plays conservatively, then sticks around forever. Give them a leadership position and it's even worse. Anyway, it seems like liches encourage this particular set of behaviors. No age death, and lots of ways to keep themselves alive that someone like a balls-to-the-wall warrior lacks. Why doesn't this happen more often? I think because the person playing the character decides not to let it end up that way. At least, more often than not.

If you've read my rambling this far, I'm impressed! My conclusion, or the tl;dr version:

We don't need any hard-coded fix to super-powerful characters. Very powerful characters can add a great dynamic to the game. The solution is to have occasional imm intervention when it's needed to make sure these sorts of characters don't fall in to conservative stagnation. That could take the form of removing someone from leadership, or it could take the form of a roleplay conversation to light a fire under their ass, or whatever else may be appropriate for that situation. So to the imms: please remember to shake things up every once in a while, if they get too stagnant.

Aarn