We suspect that someone would die in the season finale, and most people think it would be Flame Princess. Now, most of you WANT that to happen, and then the rest of the FP haters won't care. But what if it really does happen? Haven't you thought of the outcome of this tragedy?
I mean, first of all, Finn would be so devasted and heart-broken, he wouldn't never be able to be in an adventuring mood again. You might think, "Nah, he'll just get over it." You're telling me if someone you cared for and you were going out with just died, you'd feel better? He was crying over Bubblegum rejecting him, so he'd be worse if Flame Princess were to die. It would leave a hole in his heart similar to the one Billy had. He would retire from adventuring, making all the evil in Ooo destroy the land itself.
Then, the Flame King, upon hearing about his daughter's death, would become enraged and furious, getting in wars with the nearby kingdoms. Soon, most kingdoms would become burned or melted, especially the Ice Kingdom.
And last, Princess Bubblegum would become overrun with guilt. She would think she should have kept her safer, and that these wars would be her fault. Depressed, she would lose control of her kingdom, leading to a depression.
It would be the end of Ooo as we know it. And that is what would happen.