Just like the space shuttle, redundancy is the only real answer to electronic failures. No matter how one creates and uses backing tracks, sooner or later something will fail no matter what sort of equipment you use.
Other than a complete PA failure the last resort backup is a guitar amp and a very loud vocal...lol or an instrumental till a break to fix the issue.
I have never had a PA failure. I always carry a backup guitar amp and two or three guitars. Extra microphones and chords. Chords fail pretty often if you don't know how to take care of them.
I also am on the hunt for the best equipment/processes I can afford for a duo. I want to use Auto-Tune and other computer-based FXs plus the backing tracks. Auto-Tune requires a different setup for every key change for example but is programmable with midi. It also can cause problems when you are just talking.
I am finding really good backing tracks are not easy to acquire unless you can play all the instruments or have tons of money to have studio musicians produce them.
Reliable equipment exists but the better you get the more it costs in general.
Having a setlist pre-programmed with midi and a way to pause it and micro loop with a footswitch and stuff like that gets really complex....at least to me.
Bob "Notes" has been doing this for years and is a good guy to ask about these issues.
My younger friends use their iPhones for everything. I would pitch mine off the nearest bridge if I could get away with it. I really dislike the thing. Old guy thinking...lol
Here is a video that has some good ideas for a simple setup.
https://youtu.be/GGRgkYFTR_kBilly