How would you handle a game in the Revelations scenario if the players decide to work for and support the antichrist?

I would let them do as they will.

If I wanted to make it short, I'd have Team Evil graciously accept their offer of support and then just kill them where they stand. "You have been a great help by not running away, thank you for your service."

If I wanted to draw it out, I'd let them join up with the Antichrist and run amok, killing and maiming and otherwise facilitating the apocalypse for as long as the group was still entertained by that process. (Potentially running for multiple sessions, if everyone was still keen on it.) Then, when I could begin to sense the players' interest in the game fading, I would wrap it up, bring the apocalypse to an end with the ultimate destruction of the entire globe, and then have a little epilogue about the players being tortured forever in Hell.

What?

You thought you'd get a free pass just because you volunteered your soul instead of selling it?

That's not how it works, son.

Do they support the Anti-Christ because they simply want temporary power or do they ideologically oppose God?

Are they playing themselves?

How do they believe they can escape the ultimate torture of eternal damnation? Is that the goal of the game?

This is an interesting premise, but it needs to be fleshed out with a beatable antagonist and decision points that really rocket home the message that consequences are for the weak.

Ideas: A holy rolling veteran tries to kill the PC's, (rightly) believing that God is telling him to.