Well, the answer to that lies on the island of #Ireland. Due to the GFA, there are not many ways of squaring the circle of having the hard border that is required by the WTO, Northern Ireland remaining in the UK and the UK being outside the customs union.
1 - call a border poll and let Northern Ireland and the Republic reunite as a single entity. While the Conservatives are nominally the Conservative & Unionist Party, there are many who would not share a tear at the loss of NI....
2 - Stay in the EEA while joining EFTA. The UK knows that there is no technological solution short of unicorns with iPads - and iPads are expensive.
4 - Breach the Good Friday Agreement. Would May risk a return of violence? It may not come about but it would be a hell of a risk.
So, EEA/EFTA (or Norway) it is.
@theresa_may has been very clear that there will be no re-run of the previous referendum and, despite all evidence to the contrary, she is not completely daft. She can dance though and dancing on a pinhead will be required here.