Eh, i'm not so sure. I just did a quick doodle.

My opinion is that when a collision happens, it's probably very unlikely for each fragment to actually stay on a stable orbit around Earth. Chances are high that it gains a lot of energy and the orbit is significantly distorted. Now, if an orbit is already very close to Earth, that means that any distortion will make it not fit tightly around Earth anymore, instead will make it go elliptic and therefore on trajectory of collision with Earth. The only way a fragment would not do that is if it's accelerated perfectly sideways, in which case it would continue to circle around Earth for 10 years before deorbiting due to atmospheric friction. So, the cascading is a bit limited.