A show makes a 3 pt major, JUST. But if one of the dogs is excused does the major still hold?

Unfortunately no

Yes and No. If there is major in bitches and the dog goes BOW he will get a major even if the major did not hold in dogs. Also there is the specials to take into account but I am not good enough to figure this out.

If the major in dogs breaks by one dog but there is a dog special and your dog goes BOB then your dog would have a major (the special would count with the class dogs).

If the class dog goes BOB any male and female specials would be added to the count.