Question: Do the satellites fully disintegrate? What is the approximate maximum particle size of any leftovers? e.g. Will remnants ever not fully disintegrate and land on earth (people, buildings etc)?
100% of the Starlink satellites burn up during re-entry. End-of-life satellites are intentionally deorbited. Failed satellites are in such a low orbit that they will self-deorbit after 5 years due to atmospheric drag without their orbit being boosted.
There was concern at one point that the laser component of Starlink woulldn't burn up during atmospheric reentry. I don't think many (if any) satellites currently in orbit have that laser module (which will be used for satellite-to-satellite communication, and IIRC better latency by removing a necessary ground round-trip when the satellite leaves radio "line of sight" with your antenna; I don't have the correct terminology). I don't know either if that's been fixed
At the moment, only satellites in a polar orbit have the laser module installed, which I believe is a grand total of 13 right now.
Satellites in general when de-orbited are targeted to de-orbit over the south indian ocean normally, regardless if any pieces may survive re-entry.