Whatever the outcome of this Brexit mess that Cameron left the country I am pretty sure TM will see it through. I'm sure none of the other Tories have the guts to challenge her, if they did it probably would not change the outcome one jot.
It is clear that Barnier wants to continue negotiating with the existing team and is making encouraging comments to bolster TM at home. A new leader would mean a new team which would sink any chance of agreement, the EU want an agreement, albeit one that leaves them pulling the strings. That is the problem, I don't believe Parliament will accept a deal with strings, so MPs vote the deal out and still nobody challenges May - let her hold on to the poison chalice and take us out.
There is one other reason that "strings" will sink the deal, the EU will want a guarantee that the UK will not start the whole process again in 5 yrs time or even 25 yrs