Inhumans hasn't been cancelled, but it no longer has a release date. Disney confirmed today that the movie is no longer set to hit the big screen on July 12th, 2019, and they've yet to announce if another Marvel movie will take its place. With Spider-Man: Homecoming set to be released next summer, that would be a pretty perfect slot for the sequel to open in, but that probably isn't a decision Marvel Studios and Sony Pictures will make for a while as they'll no doubt want to see how the first performs.
In a recent interview, Kevin Feige had this to say about their current plans for the property. "Since we made our initial phase three announcement, we added Spider-Man, which was a big joyous coup for us. We added Ant-Man and the Wasp, which was a big fun continuation of that story for us. Walt Disney Company has announced an Indiana Jones film for right around that same time. So I think it will shuffle off the current date that it’s on right now. How far down it shuffles, I’m not sure yet." Based on those comments, it could be that we're now getting one less Marvel movie in 2019, but time will tell on that front. What we do know is that the wait for Inhumans just got even longer.