The National Professional Basketball League was really the last post-war era attempt at another major basketball league, and it's failure, along with the ABL's concurrent dissolution, showed there there was really only a market for one high-tier basketball league in the United States. It would not be until the 1960's when there would be another attempt to match the NBA.
Here are the players of the NPBL by the numbers:
Number of NPBL players: 122
Unidentified/unknown whereabouts: 4
Surviving NPBL players: 10. Definitely possible that of the 4 mystery players, a few could be still alive. Until I am able to identify them, though, it looks like we have ten survivors, six of whom also played in the NBA.
Of the 122 players, 11 players (9.02%) lived to see the age of 90. (Five living player are still in their late 80's as I write this, so this number should tick up a bit in the next couple years). Eight men (6.56%) died before the age of 50.