I don't have a cluster handy to check, but have your tried using "more system:running-config" to see if the cluster key will print out in plaintext with that command? I've used that often to get plaintext pre-shared keys for VPNs.
If you let all the active connections that went through the slaves re-establish via the master it should be minimally disruptive. I think you'll still lose some TCP connections though end users might not notice it.
I'd open up a TAC case to be safe.
