I've been pondering some ideas for a cyberpunk MMOG that involved both permadeath and Seed's injury system. Another option was, even after your body was (almost) completely destroyed, you could "go cyborg", gradually building a new body - provided you could somehow get your brain saved. Even after that, you could successfully die, but that'd be pretty hard.
Another possible option is a system from a Russian sci-fi novel I read some time ago. Basically, there was a way to buy "resurrection". It costed pretty much (But was affordable), but you could only have one "resurrection" at a time. If you ever died, you were immidiately reconstructed at one of the "resurrection" centers, retaining memory of all but the last couple of minutes before dying.
In a MMOG, this would mostly save a character from accidental dying, but if someone would ever decide to kill him for good, that wouldn't be too hard.