Oddly, I don't think it's the DUP that will rock the boat, unless there are legal complications from the Good Friday Agreement. IMO, the potential comes from the divisions in the Tory party over Brexit, more so when things start coming back to Parliament to be scrutinised/voted on.
I agree, May won't be the leader come a general election. But there is no guarantee that they will choose someone better. Most of the potential candidates are either freaks, awful or freakishly awful.
For the yanks and Trump, see us and Brexit. Only, in 4 years, they can vote Trump out if they don't fancy it anymore. If, in 4 years, Brexit turns out to be bad for us (and I'm not saying it will, before all the leavers start crying) then we are still out. So the British can/will take a punt just like anybody else.
Hopefully, May will do enough damage to the Tory party that they won't recover in time for the next election.