Hey! I'm thinking of writing a short-ish TPATQ-style AU piece, and wondered if I could grab your thoughts, as such a great ASOIAF thinker! My rough POD is, following the Tourney at Harrenhal, an hour before Rhaegar "fell upon Lyanna Stark", Rhaegar's horse takes a tumble and the Prince of Dragonstone breaks his neck. Do you have any ideas as to how politics of the 7K might play out? I'm assuming the SA bloc won't all be plain sailing, for one thing...
Well, in the absence of Rhaegar, Lyanna never runs away with him, presumably thinking that he had forgotten about whatever pact they had made to meet or had decided against it. She’s still engaged to a man she very decidedly does not want to marry, but now she has no crown prince to marry instead and escape her arranged marriage. (And while Lyanna might have tried to find someone else to marry, a marriage to the crown prince would have been so much obviously higher than a marriage to Lord Robert that - at least, perhaps, in Lyanna’s hopes - RIckard could not successfully protest it.)
With no “abduction” to protest, Brandon never has to ride for King’s Landing, which means he marries Catelyn in a timely fashion (Littlefinger, unfortunately, is probably still left alive, though this may not be as great a problem as IOTL). If I’m right and Lyanna’s marriage was set for both cultural and political reasons for later in 282 AC, after Brandon’s, then she might have then proceeded to Storm’s End, to be married to Robert - possibly accompanied by Brandon and his new wife, more remotely perhaps by Rickard, almost certainly with Robert and Ned coming together from the Eyrie to meet her at his ancestral castle. Lyanna is unhappily married and becomes Lady of Storm’s End. (It’s possible that Hoster - having by this point discovered Lysa’s pregnancy and forced an abortion, hastily works to secure a marriage with either Lord Arryn or his nephew Elbert - still alive in this timeline - both to cover up the indiscretion and to secure her as great a posting as he had her sister Catelyn. Jon Arryn may or may not have been interested in taking a new wife (he had already named Elbert his heir, and after two childless marriages may have accepted he would never have children), but a Tully of Riverrun was both a great prize for nearly any House and a means of emphasizing the Stark-Tully-Arryn-Baratheon alliance - and if Elbert suspected his bride was not a maiden, well, Hoster might have cited Cersei’s comment IOTL.)
In King’s Landing, Aerys has to deal with the death of his son and heir. Rhaegar’s only son, Prince Aegon, is maybe weeks old, no more than a few months; Aerys’ second son, Viserys, is around six years old. By strict reading of the law, Aegon should come before Viserys, but the by-now deeply paranoid and insane king is not going to sit quietly and let his despised Dornish daughter-in-law and his half-Martell grandson take power at his death. Instead, I’d think he’d declare - as he seemed to do IOTL - that Prince Viserys was the new Prince of Dragonstone and heir to the Iron Throne. Aerys might have been pleased to do so, but his legal right to do so may not have been as clear as he believed: after all, the last time a legitimate, dynastically superior male-line grandson had been displaced in the succession, it had taken a Great Council to name the new king, and the right of a king to name an heir outside traditional succession rules had, in part, led to the bloody Dance of the Dragons.
The members of the southron ambitions bloc might have seen this as an ideal opportunity - the chance to challenge the king’s (arguably) illegal change in the succession, and by that argument present their grievances against the historical caprices of the crown. Certainly, they’d have on their sides those who had backed Rhaegar in life, most notably the Prince of Dorne - after all, he’s already lost the opportunity to see his sister made queen, he’s not going to accept his nephew being disinherited. The combined heads of the North, Stormlands, Riverlands, Vale, and Dorne might then pen a declaration to the king, essentially stating that they formally protested the king’s actions and that would look to depose him if he did not restore baby Aegon to his blood rights. Predictably, Aerys would name them all traitors and call for their heads, but then the question would become who would play their headsman; the Westerlands under Tywin are absolutely not going to fight for the king who continually publicly humiliated the lion of Lannister, and while the Reach has no obvious ties to either side, its position sandwiched between the pro-regency Riverlands, Stormlands, and Dorne would make Mace Tyrell very uncomfortable drawing his levies for the king. If there were any sort of war, it would not last long before the protesting lords managed to depose Aerys II and install the infant Aegon VI. (Because Aerys had lost the right to rule, I’d guess the victorious coalition would say that extended to young Viserys - but to be safe, they’d probably want to pack him off to the Wall post haste.)
Now the victors would have some political negotiating to do, and this is where real tensions might start. I would guess that, in Prince Doran’s mind, there should be only one regent - his sister Elia, mother of the new king - with maybe himself as the baby’s Hand. But Rickard, Hoster, and Jon (and Tywin Lannister, presumably) would likely have thought they had come too far to simply hand all power to the Martells. There’s precedent to a regency council of lords from different regions, but that only secures the bloc power for as long as Aegon VI is a baby; once he grows up, there’s nothing to stop him being another Aegon V or Aerys I. What I might guess would happen is an evolution of this, something like Henry VI: a council of regents as with Aegon III, but giving itself so much power, and leaving the baby king so politically weak and uneducated that by the time he did come of age, the kingdom would have grown used to rule by a set of nobles and allowed them to retain power.