#rijl

1. He sleeps/binge drinks/otherwise disengages from the world straight through to the start of S3.

The Crowley of S2 is, in a lot of ways, more stable than the Crowley of the Crowley of S1, but I think he's also more depressed. His only purpose was survival from the moment he Fell to the moment he and Aziraphale quit their jobs, and now that he has to live, he's completely directionless. He doesn't understand (and has never understood) how he fits into the universe, how angels and demons generally fit into the universe, and what the point is if God can just wipe them all out for any reason. He doesn't believe in any part of the Good/Evil system. Aziraphale leaving--and confirming some of his greatest fears about the foundations of their relationship along the way--could be enough to send Crowley into an apathetic coma for a bit.

So I can see it happening, but my instinct says that's not where they'll go with it. Crowley tends to fall back on his escape methods only when he truly sees no other way out. In S1, he tried to drink himself to death only when Aziraphale was gone and, to his knowledge, there was no way to locate the Antichrist and even try to stop Armageddon. A few episodes before that, he proposed leaving only because Aziraphale hadn't shared Adam's location, and because Hell was actively hunting him. Once he learned where Adam was--once there was a sliver of a chance to save the world--he drove through Hellfire to do it. Crowley's not afraid to work through tough situations, he's just always aware of how fragile things are, and is prone to feeling angry and hopeless when he sees no path forward. And of course he is--it's his oldest wound, and his deepest, that he and everything he loves will always be at the whims of ineffability, and that there's nothing he can do about it.

But in S3, since he's not at the point where the destruction of the Earth seems inevitable yet:

2. Crowley will form his own plan to stop the Second Coming.

This is what I think will happen. Crowley loves Earth. He loves humanity. He was the one to talk Aziraphale into stopping Armageddon, the one to toast "to the world" at the end of S1. The planned destruction of the universe is the exact thing that caused him to Fall. Crowley is his own person outside of his relationship with Aziraphale, and that person has a long history of fighting and scheming and suffering for the sake of humanity.

He's also a very active character. He is consistently the one making plans, moving the plot forward, trying to enact change. He saw the schematics in Heaven, and I really do think he'll do his best to come up with a plan to stop them, even though he's understandably very upset.

I don't think it'll be a good plan. If I had to guess (without knowing any specifics of the plot) I think he'll either try to disrupt the delivery of Christ to Earth or try to cut Heaven and Hell off from Earth entirely. He has no allies, no support, and very little reason to be cautious in his approach, which leads me to why you probably sent this ask:

Option 3: As above, only this time the plan is either not something he plans to survive, or his own survival is not something he is particularly concerned about.

So the thing about Crowley is that I really don't think he has any substantial issues with self-loathing, or any active desire to do himself harm. He is a survivor; he values safety and contingency and isolation above most things. But he values three things more: 1) freedom of choice, 2) Earth, and 3) Aziraphale.

He's a very angry, very impulsive person, and he is dealing with a lot unresolved feelings on the issue of demons and angels existing in the universe at all, and he loves Aziraphale and the Earth so dearly that sometimes he doesn't think straight. He's reckless, he's pissed off, he's feeling hopeless, and, after their fight, he's also convinced that Aziraphale would probably be able to move on from losing him. (In his mind, 'Crowley' is not the person Aziraphale would mourn; he would mourn the dead angel he's been chasing since the Fall.) If a plan presents itself that would be dangerous to him, I think he would see no reason not to try it. If you've gotta go, go with style.

So, yeah. I don't think it's likely, for all sorts of reasons--this is a comedy show, a Bible parody, and the tone is always going to be a little lighter than the angstiest possible conclusion, final fifteen aside. But the self-sacrificial route is one I can see Crowley taking, and his inevitable survival and reunion with Aziraphale would have an aftermath that would be messy and painful and fascinating to watch. It would also have some obvious thematic resonance with Christ, a figure I assume they'll be exploring quite a bit in S3, so that would be kinda cool.

(Thoughts on the Duke of Hell theory, with a general warning it's not my favorite, so don't read if that'll upset you:)

Very much not for me, sorry. Crowley, for all he is a master of on-the-fly (ha) bullshitting, is not suited for playing politics. (Neither is Aziraphale, for what it's worth.) Crowley is too outspoken, too honorable, and too prone to fits of temper to have any patience for that kind of role. Besides that, he absolutely does not want it. He hates Hell just as much as he hates Heaven. I don't think he would ever go back to either of them, consequences be damned.