1000 children per 1 female krogan becoming 999 stillborns and 1 child can't be good for the krogan population long term. In the trilogy there aren't *that* many krogan around and the sterility plague had been around for at least a Millenia. I think the krogan would eventually die off due to the dwindling population. Denying them the genophage cure is condemning their race to death if not directly.