Well, I'll skip introductions, because I'm sure we all know what the slippery slope concept is, and how it can damage a game.
Demigod suffers from this quite a bit. Get 2 levels higher then your opponent, and things can get much worse much faster. However, that leads to some issues with Demigod. Because of the long nature of the games, they tend to get pretty sad once this hits. It's either a slaughterfest or simply boring as hell once the players start moving along the slope. In order to fix that, I suggest one of two things (or both!)
1. Give teams the ability to concede defeat. Fairly simple. Of course, the decision would have to be unanimous. Basicly, a way to end a game once things get stupidly one sided.
or
2. Balance things in such a way that the slippery slope can be avoided, so that teams can still have a chance at victory, even after things have gone south.
Either solution would be fine. Just as a way to get out of games that end up being a mindless loop of die>respawn>die>respawn>die....