A Nazi leadership fleeing when France is still mostly occupied would be seen as a betrayal of Germany, and Hitler probably knew that enough to hang on in Berlin until the final moments. In the event they do bolt, I imagined that German resistance would either crumble instantly, or the July Coup plotters seize the chance to take control and mount a desperate defence, possibly trying to capture Hitler and Co. and use them as bargaining chips when negotiating with the Allies.
In all respects, however, Nazi Germany is effectively doomed. They can try to run somewhere, but there's next to no chance of a Nazi revival now, at least not with the return of a leadership that had shown cowardice this early. Whichever SS holdouts that remain would either make up any sort of excuse to maintain Hitler's status as their leader, or simply repudiate him and claim to follow 'true' National Socialism.