Cyril Rowe, 78, was sent to prison after being convicted at Bournemouth Crown Court in Dorset of three counts of indecent assault during the late 1970s and early 1980s in Tower Hamlets, east London.
Victim, 47 year old Michael Kelsick died of motor neurone disease in a south London hospice before knowing his abuser had been convicted.
Judge Peter Johnson said: "Michael was diagnosed with motor neurone disease in 2015 and he wished to see justice done.
"He wanted to see justice done, but tragically that was not the case as he died shortly before an officer arrived to deliver the news."
Via videolink and a taped interview, Mr Kelsick used Eyegaze technology to tell the court he had suffered abuse 20 times at the hands of Rowe at St Matthias' Church between 1978 and 1982.
Turning to Rowe, Judge Peter Johnson said: "You have shown absolutely no remorse and very little insight into the harm you caused to a little boy."