Life expectancy for TOF with absent pulmonary valve syndrome

My son is now an active 4 1/2 y/o with TOF, absent pulmonary valve syndrome. He had his repair at 5 weeks of age and had  a difficult recovery. He was on/off the ventilator for multiple pneumothorax, had multiple chest tubes, develped chylothorax, etc. His left pulmonary artery was coming off of his aorta and his right pulmonary artery was huge. The right pulmonary artery was plicated and the left attached to the main pulmonary artery,VSD closed and a monocusp valve placed. After having said all that, my question is...what is his probable life expectancy? I know anything can happen, but the only information I can find on it is looking at infants before/immediately after repair. Are there any studies/information out there about these kids down the road?? As I said, my son is doing ok from a cardiac standpoint, we are just doing echos etc.. to watch and see when he will need a valve replacement. Not a day goes by that I don't think about this, just wondering what your opinion is and/or what your experience is. Thank you so much for your time. I really appreciate it.

Nicole