For one thing, the degree of disabiliity, and the degree of repair which is possible in the case of spina bifida, cannot be diagnosed before birth (or for quite awhile afterward.)
Second: if one of their two other children had a disabling disease or injury (this can happen in a flash at any playground or swimming pool or at any busy intersection) would she kill the 2-year-ol? The 7-year-old? If this woman's husband became impotent, would she kill him?
I'm aghast.
This seems like a good place to reference this recent article:
http://www.firstthings.com/onthesquare/2011/10/hope-and-homosexuality
***Because sex is not a free-floating good but a component of the call to marriage, celibacy must be the norm for many people. (***) He is also aware that marriage and parenthood carry their own burdens. Neither marriage nor the rejection of marriage guarantees happiness. Sexual intimacy is not a certain cure for loneliness or for anything else that goes wrong in the tragedy and comedy of human existence.***
Maybe just divorce him. After all, Pat Robertson says that if a spouse can no longer perform the roles for which he/she was contracted (as it were), it's the same as if he were dead.