El_Don
Unless is as bad as the cult of worms? Like he is now a lot stronger than there. So almost anything except an army of dragons and full ancient dragon priests, maybe. Maybe Miirak is super strong here, like the dragon armpr shout makes a joke but he wasn't that strong. Jon also fought amd beat back that Vampire ancestor that was acompanied by all the super strong Ancient Vampires and even stole their princes away from Cold Hardbor.... Like I don't see much phasing him, maybe the destruction of the city, maybe he will be stuck inside the city amd all the cities in skyrim are under attack, putting indirect preasure to him as he has a bunch of family and friends. Though he can sponsor a bunch of reconstruction and also scort a lot of people out with the dare dragon troops, like in Helgen.
So for the Death of Elisif the Fair was planned by the Dragons and Jon at the same time. I am guessing the plan the Dragons had wasn't accounting for him being present in the reunion place, with the power to wipe out all 100 assassins they sent without suffering anymore lost. Well that's yet to be seen but the odds of the sent attackers are not that great.