Ah man... I can't wait haha!
If he's back as evil god, he'll finish Raiden in a second.
But if he's back as himself, I imagine the dialogue will go like this:
LK: "Traitor!"
LK: *shoots fireball at Raiden*
LK: "Do you have any idea what you have done? What you have caused?"
Raiden: "I... I know how you feel, Liu Kang. I..."
LK: "You know how I feel? Really? You have no idea what I am feeling right now, Thunder God. Is this still even your rightful status after everything you have done? After everything you have destroyed?
Raiden: "... am sorry. Forgive me, Liu Kang. Please. We must move on and fight the greater threat. Shinnok has..."
LK: "Shinnok? The only threat here, Raiden, is you. You clearly cannot see what your actions can cause. Why do you think I should be concerned with something you are responsible for? Why should I again be your puppet?!"
Raiden: "Because if you do not help us, the world as we know it shall be destroyed. Shinnok has escaped and is attempting to seize control of all the realms, including our own."
LK: *looks around*
LK: "And what is there left to save? Look around, Raiden. The world is already in ruins. How much worse can it get?"
Raiden: "Liu Kang, please."
LK: "Enough of this. I have helped you too many times and what is the result? I am done with saving the world. Now it's your turn!"
LK: *walks away*