For a lot of stuff there's redundancy too— like rovers with six wheels but that can drive with any four, and the Curiosity and Perseverance missions having dual computers and dozens of cameras. I'm sure they run scenarios where significant chunks of the rover's systems fail and they figure out how to carry on anyway— thinking in part here of the famous HGA issues on Galileo:

https://en.wikipedia.org/wiki/Galileo_project#High_gain_ante...