Balon is a weird case, because he’s really operating outside the norms of medieval politics. As I’ve said before, Balon has basically decided ahead of time that he’d rather sacrifice Theon than be restricted by his hostage status, which is not someone with only one male heir would normally do.
Now, clearly Balon intended that Asha would be his replacement for Theon, although I don’t think it’s necessarily out of any enlightened philosophy on gender egalitarianism but more a kind of Viserys-like belief that he could defy the norms of his society combined with a belief that if he raised Asha to be everything a male heir should be (an experienced sea captain, a fearless warrior, a cunning pirate, etc.) that she would be accepted as one. As we see in AFFC, that didn’t quite pan out.
But there’s an extent to which, after his older sons were killed at Seagard and Pyke, I think Balon subconsciously didn’t care about what happened after him.