Is it permissible for one to marry someone who, due to some medical treatment to save their life, is physically incapable of having children?
It is very good that you are asking and trying to find out what you are supposed to do. This is a serious question, and the answer can only be given, in personal consultation with a competent Rov, in a personal individual manner.
I would suggest that you can Horav D. Cohen of Cong. Gevul Yavetz 718-252-7423 or 718-376-7388/7423.