Reading all the news about Greece, thinking about how Bitcoin could be the alternative, got me thinking about whether the Bitcoin system could ever be frozen due to non-activity or a community consensus - could the blockchain be frozen?

If I understand correctly, miners validate transactions which then create the blockchain (or blockchain history, forgive me if I'm using the terminology incorrectly).

What if the miners decided to stop working? What if the community decided to stop validating transactions? Wouldn't that freeze the blockchain and thereby put a halt to bitcoin the currency?