jmartkdr2
Hero
Even in my experience, when playing Dungeons & Dragons (tm) - campaigns don't end because of the system. They end because real life gets in the way of scheduling. Even at high levels, if you find the system isn't working for you anymore, you tend to find a way to wrap it up quickly so you can make new characters at the fun levels.I've had a number of failures out, but like I said most weren't duration-based reasons, other than the one game system that turned out to break down much earlier than you'd expect (actually, if you count D&D 3e you could argue two).
I can imagine something like Rifts going so far off the rails that even that isn't really possible, but I don't think that's common.