I don't know about Voyager in particular but spacecraft typically have multiple failsafes and backups; one example of which would be that if it doesn't receive any commands for a period of time then an automatic reset is triggered to the last known good configuration to guard against this kind of operator error.
As has been rightly pointed out this does depend on the craft having sufficient power and control to recover, but the operations teams I've encountered are highly skilled at working out what a partially defunct and beyond end of life machine is capable of – similar to some here I suspect!
See also the ISEE-3 reboot project, where a team reconstructed obsolete communications hardware and re-established contact with a mission that had ended some 15 years earlier.