In June 1405, Henry IV was stricken with a sudden case of leprosy while traveling in the North of England. He eventually pulled through OTL, but his health was never really so great. What would happen if that bout of disease was the one that killed him? Would it greatly damage the Lancastrian cause? People already believed that Henry IV's illness was God punishing him for the execution of Archbishop Richard Scrope, perhaps if it was fatal then that idea would gain more traction. Maybe Edmund Mortimer, Henry Percy, and Owain Glyndwr will be able to successfully push the idea that the Lancasters were illegitimate usurpers, with the chaos giving them enough breathing room to reorganize their forces.
On the other hand, it might not impact the Lancastrians much at all, since it would mean Henry V takes the throne early, and he by all accounts was much more competent and charismatic than his father ever was. Thoughts?