If you are talking about AROTC. Failing to qualify during Advance Camp will not result in disenrollment.
If you are speaking of Army ROTC, I would defer my answer to one of our ROO members here (Clarkson or Mohawk) as my DS is a rising MS III and so your son is a year ahead. The Dean's list is a big help as it adds a lot of OML points.
My best guess is that failure to pass one event will not be a game changer. Your DS/DD may get an opportunity to remedy the skill back at his battalion this Fall. Don't get me wrong it might impact his OML, but I would not lose too much sleep over it. I would advise your cadet take a shooting course during his summer break. The best thing to do is for him to reach out to his ROTC advisor back at his battalion when he returns.
It is also my understanding that Advanced camp has changed over the past few years.
Here is another couple of threads on a similar topic: