Close monitoring of the roots in sphag and repot if you see root issues starting. I have made lots of extra cuts in my clear pots (along the height of the pot and also increased the size of the bottom hole) that have the sphag. It seems to help the sphag to dry faster.
A repot to bark mix, IMO, is always preferable to being is sphag. Of my 140 orchids, I have 3 in sphag. Once their blooming cycle's are complete, I will move to bark mix unless I see bad roots sooner. The I'll act immediately and repot.