It’s not Kessler Syndrome until it’s so bad that we can’t feasibly launch anything new. A single cascading collision chain might calm down again after breaking a lot of stuff without any catastrophic long term impact if all the debris ends up either in a stable orbit that can be predicted and avoided by other objects, or unstable orbits that decay until the debris falls out of orbit.
It’s not Kessler Syndrome until it’s so bad that we can’t feasibly launch anything new. A single cascading collision chain might calm down again after breaking a lot of stuff without any catastrophic long term impact if all the debris ends up either in a stable orbit that can be predicted and avoided by other objects, or unstable orbits that decay until the debris falls out of orbit.