Yes, nature has the capacity and creativity to crush us.
No, at the very least we have the numbers to carry on.
There are any number of things that have the potential to cause mass extinctions most of which we don't even fully understand yet. That doesn't mean these things will cause a mass extinction. Humans have a number of physiological advantages that translate into the social advantage which drastically reduces the probability of the species going extinct.
Can it? Yes. Will it? No. Everything has the capacity and creativity to crush us, but we have the habit of not letting it.
There is always a small population that is immune to a disease.
They are not adapted to attack humans as we are right now. They are adapted to attack totally different organisms.