I dont think it publishes the full package when you do a run Paul 
As I understand it, it will compile the .dll’s you need for the workflows you need, but not make the full nuget, so it builds the code but not the package.
The code doesn’t actually need the .xamls at all, and so there is no nuget built containing them.
I could be wrong, but I think you are out of luck here.
Really bad news if so, thats an awful crash indeed.
Only hope I could suggest is maybe there is a hidden file (dunno if you have them visible by default) called ~Main.xaml as Studio can make a temp version when its being edited.