If Maty was replaced by someone like Rees-Mogg there is a very real chance the negotiations would break down altogether.
And in any case, it would hardly just be a matter of parachuting in someone else. It would take weeks to choose a new leader, time that we can't afford to waste. A leadership contest now would be very bloody, and I think a general election would not be long in the offing afterwards. And that would be brown troser time for the Tories I fancy, because they'd do into an election in disarray.
In short, I cannot see there being a change of leader for the forseeable future.