What if Balon Greyjoy died before AGOT?

[Dorian Martell]

Someone else would lead the IB to rebel and they would make all the same mistakes Balon did so the story could continue as written 

[TheKingUpNorth]

Theon becomes Lord Paramount- under all laws of succession Theon is heir and we only had a Kingsmoot due to Aeron being purposlely annoyed by certain Lords. Some may grumble but Theon will rule.

He will most likely be married to a Northern Girl maybe Sansa or Arya or maybe Alys Karstark or Manderly.

One or two from mainland might stay in Pyke to keep an eye on the new lord

During the War, Theon sides with Robb and raids Lannisport and gets some presitge and respect from his fellow Ironborn.

Ironborn may capture a few castle and most likely Fair Isle

Robb is unlikely to break his vows as no dead brothers to deal with and can focus on the war in the south

Jamie is less liekly to be freed as Cat still has two boys in Winterfell

Roose and Freys are less likely to conspire even with a broken pact as the Northern will be looking like major winners

Vale Lords might be more insistent to join in the war if its clear that Lannisters are going to fall

[1000th Lord Commander]

Ironborn civil war, I'd imagine. Theon has a claim as Balon's son, but has spent half his life in the North and has no allies or armies. Still, his pride would lead him to claim the Seastone chair.

Asha wouldn't let her little brother take what she saw as her birthright. She would make her own claim, though is pragmatic enough to try and cut a deal.

So I could see the various houses using Balon's children as pawns to try and get what they want. The Reader and Asha are quite close, so that's one for her. I imagine someone would use Theon as a puppet.

Euron would claim the throne himself, regardless. Aeron wants to control the lord, so he'd probably still persuade Victarion to take the chair.

Westeros would ignore it, possibly. they don't tend to regard the ironborn as much

[King Ned Stark]

The Greyjoy rebellion was crushed.  It's hard to believe that even Balon would be mad enough to attempt it in the first place.  They wouldn't want another taste of that, IMHO.  Ned, with Robert backing him, would follow the laws of inheritance, and place Theon as the lord of the iron islands, by force if necessary.

[Ser Ronan Storm]

Very interesting OP. I am not sure what would have happened on the Iron Islands. Theon would become the rightful lord, but being away in the North for 10 years, it's debatable if any of the Ironborn would take him seriously. Asha sure didn't, when he came back. I think Theon sitting the Seastone Chair would depend on whether or not he had the reluctant (but mighty) support of Ned and/or Robert.

I would like to think that Ned would try to marry Sansa to Theon to keep him close and potentially bring the Iron Islands into an alliance (assuming this is well before Robert rode North with the intent of making Ned his Hand and betrothing Joffrey to Sansa). And I would like to think that, given time with this outcome, Theon would have matured and morphed into a decent person. Sansa might have been in for an unhappy marriage though, because of Theon's womanizing and the fact that the Iron Islands seem like a dull place for women.

Not sure if Euron would return immediately in this scenario. He wouldn't have encountered the Warlocks, learned of Danaerys and her dragons, and obtained a shipload of magical artifacts yet, so how much havoc would he be able to cause if it was just him and his men?