What looks to be likely is that the Govt will go for some kind of judicial review of this new anti-no deal law. Boris was adamant he won't extend and must be doing so on the basis that they can find a legal workaround. In the meantime he will try to find an alternative to the NI backstop, possibly without DUP approval, as they are no longer effectively in coalition any more. He may even get European approval of it when goes to meet them, but it will be a token deal, which he knows won't pass Parliament but will allow him to say I have tried, it's Labour's fault that we will exit with no deal as they turned down May 3 times and me once. It will take some Parliamentary time to debate that proposed deal, plus the Queen's speech, some pressing NI issues etc., with very little time left before 31st. Opposition go for Vote of No Confidence, Boris sits on it for the less than 14 days it will be before No deal defaults. Maybe a GNU comes in after 31st, but only to announce the election and dissolve Parliament.
Next election most likely a Post-No deal election. Which will have a big impact on Brexit Party vote, on Lib Dems manifesto, slaying both of their relevance. Boris then wins a majority.
Labour's only hope is to somehow, judicially, force Boris out before 31st, and manage to get the other parties to form a coalition to get a majority. He should have taken the election offer, was more likely path than the alternative.