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.