Did Dennis and the group ever sing "In The Still Of The Night" in concert?
It would seem not. They did perform other tracks from 15 Big Ones (including the other doo wop cover, "A Casual Look") beginning in early 1976 but there's no mention in Ian and Jon's book of "ITSOTN" so far. I'll carry on up to the end of 1983 just to be certain...
And Eric's Setlist Archive was giving me grief in the pop-up department so I had to abandon my search there.
Maybe one of the experts has more to say about it later...