

They aim to actively deorbit starlink sats.
(Edit: they keep a small amount of propellant in reserve for the initial deorbit burn, and then position the solar array to give maximum drag which hastens things considerably)
As far as I know, apart from the first few batches, the “production run” of sats has a pretty low failure rate and are proactively sent to their demise.
There is an empirical way of doing it - best one I’ve seen online so far is this:
AN186 - Brushless DC (BLDC) Motor Connections