Any debris that gains energy doesn't get circularized so it's perigee is still low and for that reason it still deorbits quickly. If this happens, then LEO bec

Any debris that gains energy doesn't get circularized so it's perigee is still low and for that reason it still deorbits quickly. If this happens, then LEO becomes uneconomical for unimportant satellites for a few years. If you really need a really important satellite in LEO you can still put it there and just eat the increased attrition rate. Higher orbits will still be fine, particularly very high orbits like GEO where you can put most really important satellites if you really need them. Kessler syndrome in LEO wrecks commercial operation of LEO satellites for a few years, that's it. It doesn't stop humanity from launching weather satellites, military and communication satellites, space probes, etc. If a satellite really matters to society, a higher attrition rate increases costs but we have the means to launch many replacements for relatively small amounts of money. It's quite literally a non issue. Furthermore, it's not even likely to happen anyway because ground tracking of debris is very good and these satellites can modify their orbits or even preemptively deorbit themselves if the situation becomes too dicy. The most likely circumstance that causes Kessler syndrome is a major war in which many LEO satellites are rapidly and violently knocked out without warning. But if there's a major war kicking off, the cost to humanity will be so great that crying about satellite casualties will probably get you punched in the face for being so insensitive about people dying.