Why do you want to complicate a system solely to have a backup?
Don’t you have other backups in the form of your generator + converter? Or the engine driven alternator that can charge the batteries until you can replace the solar controller in case of a failure?
I can see having 2 if needed because the system is too large for one controller, but can’t see splitting the system for fear of a failure. I’d make it as simple as possible. Just my personal preference to keep things simple.