This came up in twitter discussions the other day.
The reign of Aerys II, the Mad King, was so toxic that it was headed for a bad end, no matter what happened. Rhaegar running off with Lyanna Stark pissed off a lot of people, but it was not technically the cause of Robert’s Rebellion – the King abrogating his duty to his subjects by roasting Lord Rickard and Brandon Stark alive in a poor excuse for a trial by combat, that was the thing that made the Rebellion kick off.
So… was that kind of mistake by Aerys inevitable? Was he so psychotic, so blinded by greed and narcissism and paranoia that he would inevitably cross the line and make it legitimate for his noble lords to rebel against his rule? We know that Rhaegar had hoped to stage a coup d’état to oust his father.
Rhaegar had put his hand on Jaime’s shoulder. “When this battle’s done I mean to call a council. Changes will be made. I meant to do it long ago, but . . . well, it does no good to speak of roads not taken. We shall talk when I return.”
AFFC, Jaime I
But does this mean that some kind of rebellious end to Aerys’ reign was certain?
Maybe, maybe not.
It is difficult to see how Aerys’ reign could have been sustained much longer, although it is also not clear that if Rhaegar did attempt a coup d’état if that would be strongly supported by the feudal lords. What is even less clear is if Jon Arryn’s plans for a non-Targaryen regime were something he was actively working towards, or something that he simply quietly ruminated over to himself.
So in a fashion befitting a lawyer, my answer to the title question is “it depends….”