There are 2 mostly distinct branches of number theory additive and multiplicative. Integer factorization is related to multiplicative number theory, but not really additive (as far as is known). This is a result in additive number theory so you shouldn't be any more concerned than say if a major problem in graph theory or differential equations was solved.

The fact that the security of a cryptosystem can only degrade over time is what I find so interesting about them. You can't just plug in a cryptosystem and forget about it. If you want real security you will regularly have to make changes.