Just one other factor about Sehzade Mustafa: when he was in Manisa as a part of his training for the throne, Mahidevran was with him. A simple PoD of Mustafa actually taking the message from Mahidevran about the plot to kill him seriously could have made a huge difference. And if Mustafa was too honor bound for court intrigues, this is where Mahidevran could be useful.