[ParvusPonte]

You can hear them today! http://www.rtl-sdr.com/receiving-dead-satellites-rtl-sdr/

tldr: satellites are retired by using up their fuel reserves in order to get them to burn out in atmosphere or "park" in a higher orbit. Some satellites have timers built in in case their receivers fail and do this automatically.

Essentially, when something goes wrong satellites stay in stable orbits as space junk, their batteries decay and become conductive so the sun starts powering directly when conditions are met, at this point we can catch telemetry from these space-age relics. Beyond cool.