Interesting possibilities here.
Anne Boleyn was pregnant. IOTL she had a miscarriage about a week after Henry's jousting accident. What if her miscarriage is butterflied away? Then England needs to wait 9 months to see if she births a boy. In which case, that child becomes the next King. Regency council dominated by Anne Boleyn and the Howards is highly probable. Though childhood death rates of that time might never see him reign on his own. I'd rate this probability at less than 5%.
Mary was the oldest of Henry's children at age 20. She has been disinherited by the 1533 First Succession Act. IOTL she inherited after the death of Edward, not Elizabeth, but some/all of that was thanks to the 1543 Third Succession Act which put her back in the line of succession. Mary would likely become the rallying point for the anti-Howard faction in England. The Howards were not much loved at this point by most of the nobility. No doubt the Howards would recognize the threat Mary represents to their (Elizabeth's) interests. Perhaps they quickly arrange her death, but more likely try to marry her off (quickly) to someone outside of England. I think the anti-Howard faction couldn't organize itself quickly enough, so I'd rate the probability of Mary inheriting at no more than 30%.
Henry Fitzroy was illegitimate, but known to be Henry's acknowledged son. He is 17 years old. IOTL he died in the summer of 1536. Perhaps this gets butterflied. He has no power base and is a bastard. Probability of him becoming the next monarch are slim and none.
Elizabeth wins, with an over 60% probability of becoming the next monarch. Anne Boleyn and the Howards have their hands more on the levers of government than anyone else in England. Mary has been rendered illegitimate by Act of Parliament. There are many forces that don't like the Howard faction, so quite possible some minor rebellions occur in the first couple of years of Elizabeth's reign. Anne Boleyn and the Howards will dominate the Regency. Its possible that over time the anti-Howard nobles will effectively mobilize and push the Howards off any council of regents. But even if that happens, by that time Elizabeth will have been 'Queen' for several years, so odds are they don't want to create waves by bumping her off.