It has eight other engines to fall back on, and engine restarts are already normal part of the return flight. Centre engine failure before the final burn starts

It has eight other engines to fall back on, and engine restarts are already normal part of the return flight. Centre engine failure before the final burn starts would certainly be survivable. It's just a question of the software using two or three engines in a symmetrical pattern for a 1/2 or 1/3 of the length of the 1-engine burn. I'm not sure if they could also fire one engine asymmetrically and use momentum and the secondary positioning system of cold thrusters to counter the asymmetry. I don't think that the software is enabled yet -- SpaceX usually press forward with the main objective first, and flesh out the contingencies later (for example, abort hardware was present during the last failed launch, and it had been tested before, but the software wasn't enabled, and they lost the vehicle).