Beis Meir ads that cherem d’Rabeinu Gershom does not apply in such a case. The cherem not to give a get without her consent also does not apply, says Bais Meir, because he only married her for the mitzvah. It is implied that they may remain married if they wish.
They may remain married even if he is married to someone else? You wrote that he paskened that cherem d’Rabeinu Gershom does not apply in such a case.
True, if he is an eino m’daber v’aino shomeia.
So in a case where an eino m’daber v’aino shomeia is the only brother, the almana remains an agunah for the rest of her life?
But has there been an actual case of yibum in recent decades?
MDG wrote above that Rav Moshe and other poskim wrote teshuvos for Sefardim who practice yibum today.