Mechanical solutions tend to be slower and also less reliable (more moving parts = more points of failure)
Aviation would just cease to function, nearly every commercial airliner is heavily dependent on computer control, to say nothing of things like the reservation systems that are also very complex (pricing flights is a very complex use case for algorithms)
Airplanes do predate computers, and there are plenty of airlines still flying that remain operable without electric power, even some commercial airliners.
Maybe, but you're talking about "a generation, or more" kind of lead time. For a good start you have roughly no pilots able to safely fly your computer-free planes and no instructors either. So once you've managed to design the controls, you need to bootstrap your education pipeline on using them.
I think you're imagining that current airliners and current flight instruction work very differently than they actually do. A very large fraction of flight instruction is carried out in planes that predate the embedded-computers era, starting in roughly 01975, and the more recent planes that carry most commercial air traffic are designed to simulate those computer-free planes as closely as possible.
Yeah, maybe there would be a huge spike in aviation risk, so instead of one flight in ten million crashing, one flight in a hundred thousand would crash, but that's still not enough for aviation to become a dominant cause of death for weekly business air commuters. People would freak out when they watched the news but only in countries that hand over the reins of society to nervous nellies would it be a real obstacle to aviation.
I was actually thinking about the thing you mentioned. While the flight properties of modern planes kept changing, we were using computers to emulate flying like a half a century old much smaller plane. Now that emulation would be gone.
Concorde is literally a museum piece that hasn't flown in 20 years, because even in retirement it was extremely old, and it is extremely noisy and gas-guzzling.
Aviation would just cease to function, nearly every commercial airliner is heavily dependent on computer control, to say nothing of things like the reservation systems that are also very complex (pricing flights is a very complex use case for algorithms)