What would happen if Edward, prince of Wales died earlier, say in 1545 and never became king of England? By this time his father was married to Catherine Parr, his sisters where put in succesion line again two years earlier. Henry's health was really bad, he was horribly obese and almost unable to walk, so he should not except that he could have another son. I don't except him to divorce again, it will be pointless. But who knows?
He could die a bit earlier too-he has broken with Rome, married six times and still have no male heir-it should be really hard hit.
So-would we just see Mary on the throne earlier? And what about Church of England, which was not reformed yet?