TCP doesn't "break" connections like that. Cleanly closing sockets breaks connections, but machines that crash or drop off the network won't be noticed until the connection times out, which is typically on the order of many minutes.

I realize that. My point is that existing locking systems work this way. For example, MySQL releases any table locks, rolls back the transaction and drops all temporary tables whenever the connection is closed or times out. This is no worse than what we already have.