I am a 22 year old male diagnosed as salt wating just after birth, I was taken off of Florineff by my endo.  And switched to a .25 mg dosage of dex, this has been about 9 months now and I have no ill effects from the dropping of florineff, only side effect I had from dex was oversuppression with increased weight gain and thing skin resulting in stretch marks.  I started at .75 mg.  It is possible for whatever reason that your son may not need the Florineff anymore, but the only accurate way to tell is constant monitoring of his levels with blood tests.  Don’t be worried about him being taken off of it.  But make sure he is checked.  Doctor’s do know a fair amount they’ve studied this stuff for years, it’s their specialty, they would never purposely put a patients life in danger.