In 1971, the race went on.  If such an incident happened in today's world there would be a red flag and everything would stop and hours would go by and maybe (or maybe not) the race would restart.

Note "snow fencing" piled on top of wreck.  In 1971, this wood slat fencing separated the spectators from the racecourse.  It provided no protection and the wood slats could become spears when shattered by an impacting racecar.