Last Seen: Being friendzoned hard by Danaerys, who said romance was too distracting while she was trying to take back her rightful throne. He was told in no uncertain terms to stay with the Second Sons in Meereen to keep the peace.
Poor Daario didn't just get in the way of Dany's plans (as Tyrion convinced her he would, anyway), he got in the way of the plot, so he had to go. But instead of being given a valiant warrior's death, he was instead made a victim of Dany's apparent single-mindedness. Which turned out to be a load of dragon dung since she shacked up with Jon Snow almost as soon as she clapped eyes on him.
Daario, meanwhile is left in Meereen - the second most boring place in Game Of Thrones - to play a policeman.
Could He Return?
The fact that he was left alone suggests there's a possibility, but a return would undermine Dany's instructions and would needlessly complicate the romance between Dany and Jon. So maybe don't hold your breath.