As harsh as it may seem, if testing shows an alpha major, there is no choice but to abort, as the fetus won't survive and it can pose a serious danger to the mother. Regardless of one's beliefs, there really is no choice. This is unlike beta major. Alpha major is not compatible with life because no hemoglobin is produced and the fetus cannot survive. You have to be prepared for this possibility with each pregnancy. IVF/PGD is also an option for screening for an unaffected embryo.
I know many people have strong reservations against abortion, but alpha major is not viable. There is no choice. But keep in mind that no more than 20-25% of all pregnancies go to full term. Most embryos fail naturally, either not implanting or miscarrying after implanting, and often because there are defects in the embryo. Alpha major pregnancies are in this category. They will not survive birth and will result in spontaneous abortion (miscarriage) or stillbirth. Because the mother's safety can be at risk, it is in the interests of the mother to abort once the diagnosis of alpha major is made.
I can only give you the facts. I do not see this as a reason to prevent a couple from marrying. The March of Dimes estimates that up to 40% of all pregnancies end in miscarriage. This fact does not stop people from marrying and getting pregnant, nor should it. I think looking at this with an honest and factual perspective can be very illuminating.