I'm by no means a catt expert, but all I see here is water water water!! Do you ever let this guy dry out a little bit? Overwatering generally leads to yellow leaves, pbulbs and rot...and you may have all three, IMHO. Let this guy dry out for a bit...mild mistings at most.
BTW, the new roots look great - so something is going right here! All is not lost!!
You may have just watered this guy before you took the picture - and if that is the case, then that is that...but what is your watering schedule like w/ this plant? I'd hope no more than 1x per week -and even less if there isn't significant drying out going on. Tell us more about the watering, and maybe we can help....you may have to rid the plant of the rotted parts before the rot continues to spread, that may also be an alternative option, and probably a safer one...