Originally Posted by shido
Can I get a quick explanation why?
You cannot stop resolving an effect during the middle of its resolution. Haku puts a copy of a Ninja into play while you are resolving Haku's effect. Even if Haku is removed from play, you must still finish resolving the entire effect. So any time Haku puts a copy of a Ninja in play, that copy will be removed from game at the end of the turn.