a. Fights his future self

Johnny looks into his future self’s eyes, and sees an irreversible vacancy. He determines that fighting him is the best option to get out of turning into a slave for Dr. Pont Du Loc, and lunges toward him.

The two wrestle with each other for a while, tossing each other around on the ground. As they fight, a white glowing orb begins to form around them. It grows from barely visible to nearly opaque, until both Johnny and Older Johnny realize it. When they attempt to detach from each other, gripping each other’s shoulders, they find that they’re unable to release their grasp, with their hands fused to their shirts. The harder they attempt to pull apart, the more their arms seem to dig through their shirts and into each other’s flesh.

As they continue to get closer, almost elbow-deep in their shoulders, Older Johnny decides to disclose some vital information at the last minute.

OLDER JOHNNY
I don’t know what’s
happening, but I didn’t
truly want to fight you.
The Doctor, he got to my head,
made me feel worthless.
But you’re truly not.
I didn’t want any of this.
There’s something I have
to tell you. Hunter S. Thompson.
I saw him. I also saw you,
at one point, when you
entered through Door 1
in another reality.
I told you to go back to
page 1, and that you might
see Hunter if you choose the right path.
He’s my old friend, he could help us.
This isn’t how it’s supposed to end.

Johnny is speechless, too busy thinking about how such a dull evening at a bar could end with him being fused with an older version of himself in a bright white globe within an evil scientist’s lab. And now he learns that this older self was friends with Hunter S. Thompson at some point, and that he could help them get out of this mess.

OLDER JOHNNY
It’s too late. It’s too late now.
I’m sorry. I wish I could’ve
come to my senses before
you chose to fight me.
Now I think we’re going to
be fused to each other forever
in some kind of Johnny mass.

JOHNNY
What should we do?

OLDER JOHNNY
There’s nothing we can do
at this point. We’re going to fuse
and become one, and when that
happens, the universe will collapse.
It’s like what could happen in
the Bradley Cooper and Jennifer Lawrence
paradox. We’re not meant to be too close.
At least, I think that’s what this is.

By now, their bodies are stuck together front to front, apart from their faces. Then their faces meld together as the white energy globe around them grows in density and diameter. The Doctor, terrified, leaves his lab and attempts to run out to sea off-screen.

Once both Johnnies are in the same body, twice the mass of a single Johnny and in the simple shape of a large ball of flesh, the entire facility around them begins to collapse in on itself, getting sucked into the globe and turned into antimatter. The cages, the other slaves, the walls, the ceiling, and everything else goes right into the Johnny mass, and then the rest of the universe follows. Last but not least, Dr. Pont Du Loc flies into the mass, all the while wondering where he went wrong in all of this. Perhaps meddling with realities and other worlds and timelines isn’t in an evil scientist’s best interests after all. Unfortunately for him, this lesson will never stick with him, as he perishes into nothing.

Once the Johnny mass has sucked the entire universe in, it implodes in on itself and completely disappears, reversing the very conception of the universe. Nothing is left in its place, simply a colorless, timeless slate that represents the relentless absence of existence.

THE END

You really fucked up with this choice, Johnny. You not only destroyed the world, but also made it so the entire universe ceases to exist. Good going. If you want to take Older Johnny’s advice and simply go back and convince him that him that he’s not worthless, and that he can change his fate, go back to the previous scene. Or, you know, page 1 is always available if you want to start over.