It's a good idea
but I have to wonder how it'd actually work in space. The two spacecraft would have to be quite close together in order for one to come to the other's aid in an emergency. If you're flying an interplanetary trajectory, you only have so much margin to speed up or slow down in order to rendevous with the other spacecraft.
I'm not knocking the idea, I'd just like to see more detail on how it'd actually work. I still believe the best approach is to build systems that can be maintained in space. That's harder than it sounds.