It can't affect any significantly higher orbit. Because of overlaps in orbital altitudes and the possibility of weird dynamics causing some fragments reaching

It can't affect any significantly higher orbit. Because of overlaps in orbital altitudes and the possibility of weird dynamics causing some fragments reaching a somewhat higher orbit, it's possible that the effects could cascade slightly above the altitude of the original impact event. The scariest things are a dead object like a rocket stage in GTO hitting the debris field. But even then, substantially all the debris will re-enter in a few months: perigee remains roughly the same.