I don't know if your son can become shunt independent but you need to know that if shunts are working well, imaging will often show stable and/or normal ventricles. Something like ~40% of shunts fail by two years, shunts average something like five years but that average is not helpful as I've heard a few people who've had shunts last decades. Blockage is most common reason for a revision but there are other things that can go wrong, just less common.