Fi didn't "technically" die, but she entered an "eternal sleep", and Link was the one she asked to put her there. That's as close to death as an AI-type character can get. It was at the very least symbolizing death. I doubt Fi will ever return to the way she was in Skyward Sword.
Yeah... and if you count Ravio, that's like 3 Links in the same time.
Add me to the list that believes Midna should not return, at least not in some kind of "reunion" sense. I LOVED her as a character, loved her snark and attitude, but I don't think Nintendo meant her to be some kind of...