If a pathogen more deadly than Covid starts to spread, eg like Ebola or Smallpox, we would have done more to limit its spread. If it’s good at hiding from detection for a while, it could potentially cause a catastrophe but most likely will not wipe out humanity because it is not intelligent and some surviving humans will eventually find a way to thwart it or limit its impact.
A pathogen is also physically constrained by available hosts. Yes, current AI also requires processors but it’s extremely hard or nearly impossible to limit contact with CPUs & GPUs in the modern economy.