ok. here is what you should do. slide the loose and rotted away outer cover of the roots away where this has happened. leave the inner root and others that have not rotten alone. i also would not reccomend cutting anything. just slide them off with your hands. then repot in a nice, fairly course mix, in a much smaller pot than you had it in previously. just enough to comfortably hold the roots. when i say a nice course mix, keep it simple, just like big bark pieces mixed with big perlite pieces at ~ 2:1 ratio. water the plant in real good and give a broadspectrum fungicide/beneficial drench if possible. then leave the plant be and keep it on the dryer side, not dry, drier, until new roots grow and the plant sends up some new shoots. this plant should be fine...