They wouldn't disappear. They would, after a period, go back in time in order to become one of the other people in the battle.

I realize that. For other observers' practical purposes, they would disappear.

Using a time turner to make clones in battle is a very, very dangerous idea. Harry has been warned, strenuously, by Professor McGonnagal that he should not directly interact with himself

Meh, she worries about that kind of thing too much.