Has an NBA game ever ended 91-79?
It has. 91-79 has been a NBA final 35 times in 73,172 games. The first was Rochester Royals beat Washington Capitols on February 15, 1949; the latest was Boston Celtics beat Toronto Raptors on March 23, 2016.
That makes 91-79 the 678th most common final score out of 3,189 that have ever occurred in NBA. One point away, 92-79 has happened 35 times and 91-80 has happened 41 times.