Two of my six daughters have used Accutane. Both had to go through a series twice, as the acne returned for both of them. One had to do "two-a-days" for a few months. Acne in our family is a hereditary problem. One daughter was not left with any scaring - the other has quiet a bit that we have had to treat with peels and laser treatment.
Each treatment round the dr. prescribed usually lasted 6 months. I felt good about that, because side-effects really escalated after six months.
Accutane is a nasty - but miraculous drug - and very scary. The side effects are many, as you may well know: night-blindness, headaches, lower back pain, dry skin, etc. My girls' grades also suffered and they both needed to be taking anti-depressants during their treatments.
It is good to take break between rounds of treatment - because it may well be cured with one treatment series. If it comes back, attack it again. Usually two treatment rounds do the trick. I hope your son does not have to go that route. But bad acne can be so debilitating socially and emotionally that at times I have looked at Accutane as a god-send.