I'm not a fan of May, but you've got to hand it to her that her brief was virtually impossible; a country divided into three parts (leave, stay, and something else). Her refusal to discuss with Europe for nearly two years only made her position weaker, although since she had no real mandate (again the country divided in three) it was difficult to give her negotiator anything useful.
It remains that the UK's political class has not covered itself in glory here...again! May was not a leader but nor was anyone else for that matter. Boris Johnson is a smart man, but he's even more of an ass than May is! The labor leader own inability to deal with this national crisis, treating the exit from Europe as "an opportunity for Labor to eventually take power" speaks volume on his own shortcoming as a real leader. The leaver's pundits with their lies didn't help either.
The departure of the UK will be a blow to the economy -- that's a fact, as is the departure of the UK automobile industry -- that sees 90% of its production destined for Europe. Britain will not find a friend in Washington, Trump or not, the UK is of no consequence to the US and will only be "an ally" when DC needs its own friend.
The UK will survive this, some pain (actually a lot of pain), but it will survive, diminished, maybe the strength of the City was too much as was the predominance of London. A rebalancing seems to warranted as so the middle class will once again pay the price, such is life