It shouldnt anything close to how it was done.

Im more of an unenthusiastic Lexiteer, so I do think idelogically, leaving the EU is a good idea, my vision of what that should be is completely differant to what is happening.

Frankly, in theory, the UK can prosper outside the EU, but that would take a long term vision, and a lot of working up to that point, until it became inevitable, and pain free, and a differant political situation to what we have.

In your scenario, well I wouldnt be a Tory prime minister, so If I was prime minister, we would by implication already have a hard left leaning Labour government, and assuming I had been in office a reasonable amount of time beforehand, would have already made inroads into alleiviating the worst of austerity.

The arguments to leave would have been differant, and the political expectations differant.

I would go ahead, recognise that it will cause massive short term distruption, to grant the opportunity to remake the country in the image you want, so massive governmet borrowing, and Social programs of the like last seen in the 1930s.

It is effectively a mini revolution, treat it as such, make all the two years about planning and putting systems in place to minimise the impact of that.

Recognise there is no deal, the talk of a deal is political nonsense, you are either in the EU or not, there are no half measures, the talk of a deal has been the most infuriating part of this, and has wasted all that time.

There can be no deal, that satisfies those wanting to leave, so no deal that isnt just a shitter version of remaining.

Recognise there never was any chance of an acceptable deal, assume no deal, spend two years making meaningfull preperations for that, after leaving inroads into joining the EEA and such are a possibility.