Personally, I think Micheal Chong would make a good conservative leader...
To the topic, Harper has said that he would go if the Conservatives lost even one seat. So I suspect he'll go. He's had a good run, and I shudder to think who will actually take his place at the head of the Cons.
I suspect Muclair will be gone after this election, unless by some chance they win.
Trudeau has a ways to go yet. It would take an extraordinarily bad showing for him to be ousted. (Like being reduced to 2 seats...)