The Senior was red-flagged after the leaders had completed their 6th laps - all riders who had been lapped should've stopped at the end of their 5th laps. According to the lap-by-lap results, there were 41 runners at the end of lap 5, of which 31 finished lap 6, so the majority completed the full race distance.

I'd heard that Hutchinson's rear brake pedal had snapped off, hence couldn't continue *shrugs*