This is by no means a sure thing. The hardcore-Brexiteer “European Research Group” (ERG) faction of May’s Conservative party says cabinet resignations are coming, because the deal involves Northern Ireland staying inside the EU customs union for a few years, in order to avoid having to impose a hard border between the British province and the Republic of Ireland (an event that could come with bloody consequences.) This is the so-called “backstop” that, Brexiteers fear, could leave the country at the mercy of European rules without the U.K. having any influence over those rules.

Even if there are no cabinet resignations, the ERG will likely try to topple May by triggering a leadership contest. There’s no certainty that they will organize enough signatures from lawmakers to make that happen, but they claim to be close. As noted by the Guardian, sterling “will either soar or tumble once this afternoon’s cabinet meeting has played out.”

Brexit was always a bad idea that was going to leave the U.K. worse off than it has been as part of the EU. The best way forward would be a second referendum to allow the British people, who should by now be vastly better informed about Brexit’s consequences, to change their mind.

That would be politically toxic, but the prospect of a “no deal” Brexit is outright cataclysmic. Supply chains would be thrown into chaos, there is a very real threat of food and medicine shortages, the British economy would probably collapse, and the Eurozone—which may be suffering growth issues (see below)—would also take serious damage.

The hardcore Brexiteers need to shake off the illusion that no-deal is a viable option, or some kind of leverage that will squeeze more concessions out of an EU that rightly sees reserving membership benefits for actual members as an existential matter. (A tip of the hat to Irish solicitor Simon McGarr, who quipped on Twitter that “Brexit has been 18 months of watching someone trying to haggle on prices with the automatic scanning machine at a Tesco checkout.”)

And Jeremy Corbyn’s Labour Party, which is threatening to vote against the deal, needs to realize that there is no more time for negotiations—Brexit is scheduled to take place in March, deal or no deal. If opposition parties are to nix the agreement and bring down the government, they need to be prepared to either swiftly produce a viable alternative—and good luck with that—or allow the British people to call the whole thing off. It’s time for everyone to stop posturing and get real, or things are about to get very nasty indeed.

A version of this story first appeared in Fortune’s CEO Daily newsletter. Subscribe here.