Open source never dies. It may lie dormant until someone decides to resurrect it. It may die when the last copy of its source is erased. That's not likely to happen, as most of it is already scattered around dozens of source-control repos.
Your assertion immediately led me to try to come up with a counter-example, and the first candidate that popped into my head was FVWM95[1]. This was a dumb choice of course, as it was a popular package in its day, and it's not that old in the grand scheme of things. I suppose there's a decent chance that a few people out there still run it on old machines, perhaps even just for the novelty. In fact, the shot of the full desktop[2] reminds me that I still occasionally use xcalc, partly because of its light weight and partly I suppose for the nostalgia of it.
To your point, I'm sure there are plenty of software projects whose last remnants exist only on dusty tape cartridges in the basements of university computer science departments. For practical purposes, it seems reasonable to call these "dead". I'd bet there are many more projects in this state than there are people willing to resurrect them. It's safe to say though that MeeGo has a ways to go before it reaches this point.
