This might be a good time to look at the alt coins. Are there any alt coins that eventually went offline, or do all alt coins continue to exist, even if they only have two users and near zero value?
A coin is officially dead only if it can't be mined anymore. I've seen a couple of coins die due to coding hiccups. Something "breaks," the dev has already split and nobody in the community is interested in fixing the problem.
If it can't be mined and blocks can't be added to the blockchain, it becomes impossible to transfer and thus its value goes to zero.
See HawaiiCoin and ColbertCoin for examples.