A plague would have to mutate very fast in order to disable a robot. However, if it was extremely intelligent, like the "noocytes" in Blood Music, it could do anything it wanted to.
On the other hand, if it was your run of the mill plague, just extra contagious and deadly/engineered to target humans then I'm sure robots intelligent enough to take out the human race would find some way to kill the parasite. So it depends.
Anyway, I'm halving the points now.
Superplague ( 5 )
Robots Attack ( 4 )