Potvin played in 262 games from 11/29/1975-1/17/1979 (Potvin's streak ended in when he slightly separated his right shoulder in a collision with the Rangers' Pat Hickey, Potvin would miss 7 games; it would be in his next game at MSG that he would collide with Ulf Nilsson)
Bobby Nystrom has the second longest streak in club history: 301. Moulson would exceed that in October if he doesn't miss a game (He would be at 294 at the end of this season). He is still not half-way to Billy Harris' club record of 576. That streak is safe until Christmas-time, 2016.
Calgary's Jay Bouwmeester has the longest current streak (and longest ever by a defensemen) in the NHL - 602 games (split between Florida and Calgary).