[keyless_]

Unfortunately, you do need _some_ sort of TTL because there is no way for the lockable server to know when a remote process has simply died.

However, TTLs can be set to be arbitrarily long (e.g. multiple days), which means, in practice, you can avoid losing locks due to networking issues.

[IanCal]

You can instead have manual overrides. Not seeing a lock means that at least a person has decided it's safe to run Vs something simply have taken too long to respond.

[GordonS]

If TTLs can be arbitrary lengths, wouldn't setting them to high values (a week, month, year, whatever) allow you to implement whatever manual override mechanism you wanted?