[Dove]

If one rover is hit by a software blunder, it's likely the other one will have the same problem.

Actually, this is something they plan for. It is not unheard of to have the software for two different devices developed by two different teams who are not allowed to talk to each other, precisely to avoid this scenario.

In fact, there are Common Cause Analysis people whose whole job is to think of this sort of thing and recommend ways to avert it.