Even with the DUP they might not win a vote of confidence, but for sure they can't win without it.
If there is a general election, you can guarantee that at least one party will put another referendum in their manifesto. And if they hold the balance, as is most likely, we get our referendum.
So, no one wins a majority and we get a referendum.
If they survive a vote of confidence, it means they got DUP support, which in turn means no withdrawal agreement.
New government escapes into summer recess.
Now they get two months to figure out how to get a Queen's speech through parliament in September.
And if it's voted down, it's a general election and the Lib Dems put a referendum in . . . etc.
Brexit is already over. There's no way it's going to get through parliament now, not under any government, with or without a general election.