Now, Heinrich never had any reason to believe he would be king of Prussia, right?
No. I mean, in theory I suppose Fritz and AW and both of AW's son's could have died of cholera or something like that, but short of such an event, there's no way Heinrich would have become King. Prince Regent, now, that was a realistic possibility after AW's death and before FW2 was off age, if Fritz had died for whatever reason during the remaining 7 Years War. But I don't think Heinrich ever expected it. Unlike FW, who spent the last decade of his life being considered at death's door repeatedy (by Fritz and other people) only to recover after all, he didn't expect Fritz to die until the year in which Fritz actually did, and by then of course FW2 was already approaching middle age.
Re: Rokoko Dragon Sickness or: Better stay away from rings of power as a Hohenzollern
No. I mean, in theory I suppose Fritz and AW and both of AW's son's could have died of cholera or something like that, but short of such an event, there's no way Heinrich would have become King. Prince Regent, now, that was a realistic possibility after AW's death and before FW2 was off age, if Fritz had died for whatever reason during the remaining 7 Years War. But I don't think Heinrich ever expected it. Unlike FW, who spent the last decade of his life being considered at death's door repeatedy (by Fritz and other people) only to recover after all, he didn't expect Fritz to die until the year in which Fritz actually did, and by then of course FW2 was already approaching middle age.