That seems to be just about the only possibility. Remain by unilateral A50 withdrawal is of course legally quite possible. But the needle hasn't moved much politically. People either don't care or are as Brexity and ignorant as ever.

On this side of the Channel too. Mind you, while the political/mental shift has happened on the EU27 side and the UK is already seen as a third country (that cannot be trusted because it keeps going back on its word), the EU27 people are still somewhat in denial about the consequences. A negative shock is not really an advertisement for Remain but rather more fuel for recriminations. Or a propellant for a suboptimal deal because it's still better than no deal. Then it would only be a question of time before people in turn started complaining about that deal.

_{Schengen is toast!}