Kessler Syndrome is a serious potential problem and it's certainly one people should be worrying about but it's mostly something that's only a problem for LEO w

Kessler Syndrome is a serious potential problem and it's certainly one people should be worrying about but it's mostly something that's only a problem for LEO where you have lots of things in a relatively small volume going very fast in different directions. Further out in MEO where GPS satellites are there's a much greater volume, fewer satellites, and the satellites aren't moving as fast. There's no way Kessler Syndrome is going to start there. You do have a bunch of Russian satellites that loop in fast and close by the South Pole then go high and slow over the North, letting them spend most of their time being visible from Russia. Debris from from a cascade could kill one of those, which would cause debris that would kill some but not all of the GPS sats. It would be a relatively slow process compared to what would go on in LEO, though. Satellites in GEO won't need to worry about Kessler at all. They're all in equatorial orbits, traveling in the same direction at the same speed. If one explodes its debris will only hit other satellites with the explosion velocity, not orbital velocity. So those should survive Kessler Syndrome fine, though you can't put any new ones there. Also, Kessler Syndrom isn't forever. Satellites in LEO need to boost every once in a while to overcome atmospheric drag. As things get broken up their surface area to volume ratio increases and the fall out of orbit faster. Air density falls of exponentially with height so the lower reaches of orbit will become safe first. The inner reaches of LEO might be clear quickly but I have no idea how long it would be before orbit was totally clear.