To be sure, the performance was not the studio was hoping for, even if reviews of the sequel were actually slightly better than the previous entry.
However, based on producer Andrew Form’s comments to Collider here, it would seem that while continuing this particular part of the franchise is unlikely, the turtles as characters probably aren’t going anywhere.
While Teenage Mutant Ninja Turtles: Out of the Shadows might not technically be considered a bomb, it made almost $250 million on a budget of $135 million, it made about half what the previous film was able to do, and didn’t even break $100 million at the North American box office.