well William can't/wouldn't marry James' daughter, because no James, assuming that Charles I's 3rd child lives to be an adult in this case, she would be married off to some foreign court like Mary and Henrietta, if its a Catholic court (like Henrietta) her children would be totally unsuitable for a bride to the Prince of Orange, and if not, well there just wouldn't be the dynastic advantages that marrying William to Mary had, any ways, different wife means different luck in the children department the problem William and Mary had seems to have been on Mary's end
any ways, failing William having heirs, it'd pass to whatever heirs Charles I's 3rd child/2nd daughter had, who might well be Catholic, to failing that, Henrietta's children, who were Catholic