Quote from: petesays on August 05, 2013, 12:35:23 AM

I was thinking about the hundreds of dead coins in the future and wondered...

Does a coin die when the last miner stops mining?

Is there a way to revive a coin or blockchain?

What happens if someone starts it up again with an old blockchain, and then someone with a newer blockchain starts?

Yes. When the last miner stops mining the blockchain dies. However, the coin dies until the last user disconnects from the network.
That way, if someone else comes online, they won't have any connections to nodes and won't be able to know about transactions to verify.
However, due to IRC peer discovery and some centralized features, if people start using a client again a coin can be brought back to life.