10+ years ago, I lived in my service area, and it was not uncommon for me to swing by my house to pick up stuff. Lunch, change of cloths, cell phone charger, etc. In addition, I worked in a semi-SSM system where I didn't have a base station, it was not uncommon for us to chill at my apartment. still available for calls, just we didn't need to be sitting in the truck for 12 hours straight. If was on a single responder vehicle, and I want to go home and have dinner with my spouse/family, while still in my service area and available for any calls, why should anyone care?
As for this topic, I don't care that they took the vehicles home (provided they were in service and available for calls), however I do have an issue with this part: "employees unplugg[ed] vehicle trackers."
Personally, I don't care where field units go, provided they are in their response area and available for calls. And if they need to leave their response area for a quick detour (getting food, clean bathroom, restock equipment, etc), as long as they let dispatch knows of their plans and why they are going (as it might impact the closest unit dispatch for an emergency call), I have better things to do than micromanage them.
However, if they are damaging or disabling the vehicle trackers, then that shows intent, and they knew they were doing something improper, and they deserved to be terminated. Maybe there are security concerns with leaving a vehicle outside of a home overnight.. but considering trucks are often parked outside, I think that's a really weak argument. But the intentional disabling of a vehicles tracking system? sorry, that's enough for me to say they should go.