Can we please stow away the Bianchi/tractor stuff, along with the snowflake stuff. There were no tractors involved with this incident. Indeed, as both cars simply broke down, no tractors were going to be needed anyway as they could (and probably were) be wheeled away.
The question is about risk. Many here seem to believe that there wasa high likelihood of a third car going off at the same place in the last two or three laps of the race. In fact, the odds of this are pretty much in line with the odds of you winning the Lottery. If you really cared about risks, you would address some of the genuine risks that are allowed in F1 all the time. Walls of human beings in the pitlane, crowds of team members on the pitwall (what if a car reared up over another's wheel and landed on them), driving standards that wouldn't be permitted in a banger race at Aldershot, cars that disintegrate into a shower of c/f shards after the smallest clash, etc etc.