Theon Greyjoy is a character that has gone through much character development. And now he's trying to ensure that Yara gains the Salt Throne, and now they plan on retaking it from their evil uncle. Their plan seems simple enough, but the even the simpliest plans so often go amiss. For I forsee a massive sea battle approaching. I predict it will be a three way battle between Daenary's and her allies, Euron and his fleet, and the Lannister fleet.
Jon and Sansa were lucky to survive the Battle of the Bastards considering the nature of Game of Thrones, but this does not mean other characters will have the same luck. Which is why another prediction of mine is that one of the Greyjoy siblings is going to die. But who? I can see advantages and disadvantages to both. Let's take a look.
Scenaio 1: Yara lives and Theon dies. Advantages: If Theon does not live through the Sea Battle, it will be a sad loss, but it could also be his crowning moment of awesome. I think if he does die, he should sacrifice himself to kill Euron. Theon dies a true hero to ensure Yara gains the Salt Throne and Daenary's claims Kings Landing and is remembered as a fallen man who became a true hero.
Disadvantages: However, if Theon dies, there might be no one to ensure that Yara will fullfill her end of the alliance by introducing the liberal policies into the Kingdom of the Iron Islands that forbids pillaging. Can Yara hold on to a Kingdom who's very culture about Paying the Iron Price is tossed aside? Without Theon's help, it will be harder for her.
Scenario 2: Theon lives and Yara dies. Advantages: If Theon lives but Yara dies, this could be a chance to show some real character development for Theon. With his sister, uncle and father dead, he is now the King of the Iron Islands and will ultimatly have to accept that responsibility. I think as King of the Iron Islands, he'd be more likely to agree with Daenarys terms and cpuld establish better relationships with the other kingdoms.
Disadvantages: However, there is a sad side to Theon becomming King of the Iron Islands. With his sister, father and uncle dead, he will be the last of the Greyjoy's. And since Ramsay cut off Theon's penis, he won't be able to procreate and father an heir. Meaning that when he eventually dies, House Greyjoy will die with him and the Kingdom of the Iron Islands will risk a civil war which could spell the end of the newly restored Kingdom.
Which do you you think is more likely to happen? Theon dies a hero while Yara survives and ensures the survival of House Greyjoy and the Kingdom of the Iron Islands at the risk of displeased subjects with the new policies or Yara taking her word back? Or Theon lives and becomes King and ensures that the Ironborn way of life will change, but at the cost of House Greyjoy's future and risking the future of the Kingdom of the Iron Islands? Personally, I'm in favor of Theon dying, but it should show the audience that he's not a coward and that he's brave.