There have been flight crew health issue fairly regularly. If you want to get really paranoid about flying, read the Aviation Herald, but keep in mind the tiny fraction of daily flights that the problems represent. Yes, the redundancy of having 2 people capable of flying the plane is worth having (plus, some planes these days can autoland, though they still need to be human-driven to complete the job and move around the airport).

That experience does not transfer, necessarily, to trains. If a train stops, it doesn't fall out of the sky. A better analogy for trains would be truck or bus drivers, with the added safety provision that most trains have a 'deadman' monitor of some kind (yes, most can be fiddled, but they usually aren't) that will stop the train (and possibly, with modern systems, call for help like OnStar does?) if the engineer becomes incapacitated. You can't just stop an airplane, so as long as they aren't fully automated (would you ride in a drone airliner?) 2 people up front are needed. Trains, not so much, and I suspect that as PTC evolves that will become even more the case. Still, until all railroads run in a BART-like isolated environment, I don't see full automation without any human aboard being acceptable in general use.

On shorter runs such as the Cal-Amtrak trains and most commuter trains, it's been one person operation for ages.