It's safe to state these fuel cutoff switches aren't to be touched in-flight unless the word 'fire' is said beforehand. Even then, you only perform fuel cutoff for the flaming engine. If the copilot was busy with takeoff, there is exactly one other person in the entire world that could have flipped both switches. We may never know which one flipped them back.
Fire isn't the only instantly severe problem with engines. Another is violent shaking if, say, part of the rotating assembly came off.
Yep. Fan blade off, shroud separation, HP disc separation, compressor stall, FOD ingestion/bird strike, EGT rise, oil system issues. Very unlikely events but still possible events that need a prepared response to and capabilities to manage the aircraft. The presumption is that the crew is trained, diligent, disciplined, and concerned with survival. Without that, aircraft would need to be unmanned and flown by AI lacking in ability to handle any unforeseen events creatively.
I'm not sure you want a creative AI flying a plane anyway.