So, in the end of the story... Gangplank lives but its secret?

Miss Fortune thinks she beat GP but here he still stands. The master of all of Bilgewater possibly escaped due to unforeseen circumstances. He could had fallen into the water as well when the blast happened and secretly survived but now seeks revenge on MF. Miss Fortune on the other hand feels bitter because it might had not been GP who shot her parents, but she believes its him due to the fact she blames his want for control for the killing. Reasons why I don't think its GP: 1) GP wanted people to fear him would not hide his face 2) burning red eyes 3) GP isn't said, nor shown to be a good shooter as he uses a knife and would rather stab each of them rather shoot them. I must say, even though you tried to wrap up the mystery, it doesn't fit well and a new champ should just be made to fill in the gap for the murders.