I think we're either looking at a 2nd referendum or a new General Election.
Even if a2nd Referendum were to vote to Remain after all, it's too late. Do you really think all 27 EU countries will agree to allow a simple return to the status quo? Britain will have to give up at least some of its carve outs to be able to get an agreement and that makes it even less likely that Britain would agree to remain.
(But I know there is a debate and the ECJ has to give its opinion on the possibility for the United Kingdom to withdraw Article 50 unilaterally)
The situation will be different if the UK is out and then asks to join again the EU.
I don't see any option in Article 50 for the UK to unilaterally withdraw its invocation. All I see is an option to extend the deadline past two years if all the EU states agree, and I suppose that there could be a permanent extension, but as I said I don't see all the other EU states, especially those that don't have a lot of economic interaction with the UK agreeing to a return to the status quo.
There isn't either any indication in Article 50 that the member can't withdraw its invocation.
The Vienna Convention on the Law of Treaties, in its article 68, indicates that a State can revoke a notification aimed to withdraw from a treaty at any time before it takes effect.
Now obviously European Law is not International Law, but if you consider that a State by invoking the Article 50 is acting as a sovereign State, it surely can, as a sovereign State, reverse its intention.
