If the ignition has shielded leads the ground is in the braid....If not the spark is going through the sensor and it will soon be gone...
Had an old C&H years ago that someone grounded the ignition through the carb mounting bolts into the bakelite carb insulator block...The C&H is good enough to make a carbon track through the bakelite to ground, and the engine still ran...
another with a broken ground wire was a Q52...You could see the spark at the gap between the sensor and the hub with the engine running...They don't make hall sensors like they used to, or ignitions either....