[gruez]

>How can I be sure that the device actually shuts down and isn’t listening to collect information for my employer?

Just... turn it off? Others have mentioned that theoretically the mac is still "on", but do you have any reason to believe that your employer will go through the effort flashing your macbook with modified firmware (which probably involves bypassing a bunch of protections apple puts in) to spy on you? If you actually think the device is bugged then you probably want to put it in a faraday cage that's also soundproof (so it can't eavesdrop on you).

>Furthermore, how can I be sure that apps such as PagerDuty or other “on-call” apps aren’t relaying my location and other metadata to my employer?

Why are you granting location permissions to the app in the first place?