If the UK crashes out of the European Union without a deal, the Liberal Democrats and a Remain Alliance can still function if they won government. Article 49 of the Lisbon Treaty sets European Law for a State joining. It needs unanimity in the Council of Ministers (heads of government), consultation with the Commission (its civil service and initiator of legislation and guide of regulations) and a majority vote of the European Parliament. The UK House of Commons would pass retrospective legislation that we did not leave. Fast action can minimise economic disruption.
A General Election would be fast because of economic chaos coming, and even if the opposition parties could not agree an interim Prime Minister, they are likely to vote down the Budget even if the Tories remained in power.
Suppose we get an emergency fortnight plus government, and it delays Article 50? I think it would also take the leave date out of leaving legislation and vote money to the EU. What is likely then?
The Conservative and Johnson would go to the country humiliated and having failed. They'd be picked off in a critical number in each constituency by the Brexit Party.
A situation will have existed where Corbyn failed to become interim Prime Minister and someone else did instead: let's say Yvette Cooper.
In order for many Labour MPs to vote her in, some will have defected as a result of not wanting Jeremy Corbyn to be Prime Minister and/ or being annoyed at his apparent selfish tactics, putting at risk getting a delay. Many would go independent, some join Change UK (as renamed) and some the Liberal Democrats.
Many Tories on the remain side will have broken with Johnson's actions and defected themselves, most I'd think straight to the Liberal Democrats. The Lib Dems will have to have worked on a Remain Alliance.
So Labour will go into the General Election is a distressed and confused position. The Conservative Party will be disintegrating. The Brexit Party might win some seats, but find breaking through difficult, and the Tories versus them will create a losers' result.
So there might be a very strong clear Remain Alliance, if it is handled well, and - surely - if it wins it is enough to declare this as good as winning a second referendum and then revoke Article 50 straight away.
Those who want to leave will have to achieve power through the ballot box and make their claim. There is no doubt that many will be uneasy with politics, but they are now. The damage was done by using Direct Democracy in 2016 when it does not work in the British Constitution - because we have MPs paid to discern and decide, who consider minorities and changes of view, even though they are guided by manifestos.