You mean a Kessler syndrome, or event
https://en.wikipedia.org/wiki/Kessler_syndrome
And to answer your question : we don't know exactly yet, but I guess we'll know pretty soon
No, certainly not in LEO. Debris in LEO falls back to Earth in only a few years so even if a shooting war started and shattered every satellite in LEO into a mist of deadly orbital speed bullets, a few years after the war ends LEO would be clear again. All of the other effects of such a large-scale shooting war would be far more concerning to everybody on the ground, space debris would be the least of the concerns for any survivors.