We know how this ends.
So, let’s assume they do vote against. One of two things then happens: the first is, others make up the numbers to pass May’s deal, it passes, and the backstop is put in place.
What happens then is chaos. NI’s economy grinds to a shuddering halt. Utter mayhem ensues in the UK transport and port system. And everyone will blame the DUP as the tailor-made scapegoat.
There is no option except movement that doesn’t see them go under a bus. And they’ve made that into a fold that will be throwing themselves under a bus.
But, this is the pattern. We’ve seen it before, in detail, and more than once.
And, as noted at the start of this thread: we know how this ends.