Is it not the case that one can back up their BC wallet into a locally encrypted file, in the event that their online wallet is compromised? I'm a user of coinbase, and have a local backup. I was advised to do just this: take a backup of my wallet, just in case something bad happened to the server. That way, I have legal recourse if push comes to shove.
If your online wallet is compromised and the coins are transferred to new keys, ten backups of the keys that USED to own those coins will be insufficient.