danny, you should have a backup copu – vegas makes one always with your original veg file. unless you ticked this option to off in prefs. other help i can give you is-try looking for autosave projects. my autosaves are here
C:UsersUSERNAMEAppDataLocalSonyVegas ProVERSION NUMBER
theu have names like 00001b60.autosave.veg
the last one you have before this fatal rendering should work. open it, re-save it under your name and that is it. always make a backup, don’t count on the system.