Aside from a total loss, losing the Green and Yellow systems is the worst case. The Blue system gives very limited services and it’s a serious emergency if that’s all you’re left with.
The loss of a single system puts additional strain on the others and whilst this shouldn’t be a problem, I prefer not to test capabilities to their limits.
I’ve had two Blue system failures on the baby bus, both due to pump failure which were a big deal. Luckily never a multiple one.