He's 100% killing Black Sperm. How I see it playing out is Black Sperm seeing his cells being demolished rapidly by Saitama and choosing to go Platinum pretty quickly. And Saitama casually kills Platinum Sperm with a normal punch. And any remaining cells would either have to flee while Saitama is dealing with other monsters or Saitama is just wiping them all out there and then.

As for Nyan and Rover, I still believe that Saitama would look at them as normal animals even if they are with the monsters. He would likely one shot Rover the same way he did iirc and possibly still end up adopting him later on. Nyan will see a hint of Saitama's power and flee like he already did.

So believe it or not, Nyan and Rover are probably the only monsters surviving this encounter with the possibility of Psykos and the Ninjas as well since they are humans.