On the Sea Vixen D3 program, completely normal controls were retained and the pilot could also fly by push buttons that mimicked the ground based radio commands.
In the event of some sort of emergency and the electronic hydraulic servo valves for the remote control became locked somehow, there were electrically fired explosive bolts for the control surfaces that severed the drone specific mechanical control links. This was activated off the stick by using the redundant "fire" button from one of the weapon systems that were of course no longer active.