There isn't just one satellite zone. Starlink satellites are about 4 times closer to earth than than they are to the geosynchronous Hughesnet satellites. The starlink satellites are close enough that even after full Gravity-style Kessler syndrome, you could just wait several years and start over from scratch.
Obviously that is something to avoid, but it's not like we're filling up a non-renewable resource in low earth orbit. It cleans itself naturally.
Note: Starlink orbits at an altitude of 340-350 miles . Hughesnet’s geosynchronous orbit has an altitude of 22,000 miles. That is over 62 times higher, not 4.
FWIW.
I apologize, you are quite correct! Not quite sure what my brain was doing there, I was looking at those same numbers and somehow typed 4.
Sorry if this a stupid question, but in the event of mass collisions a la Kessler, wouldn't some percentage of the debris get stuck in higher orbits? The kinetic force of collisions at those speeds seems pretty significant.