There are still some loyal Ironborn on Yara's side. She went back to the Iron Islands in ep 2 to reclaim them in Dany's name, also to use the islands as a base in case the battle at Winterfell didn't go to plan. The Ironborn are an afterthought this season, it is really a shame.The Greyjoys aren't exactly a force at show's end.
Dany wiped out the majority of their fleet and a lot of their men.