I removed the Ecobee built in app in favor of the community built one and it removed the thermostat from the hub without prompting me to remove any rules associated with the device before it removed it. When I recreated the thermostat, it actually broke one of my rules I had setup to catch an open door / window and turn the thermostat off.
Simply add the Builtin Ecobee suite and have it add a thermostat. Create a new rule based on that thermostat device, then remove the ecobee suite. Try to edit the rule.
I was actually surprised because I would have thought that it shouldn't have let you remove the ecobee builtin suite when a device was in use in a rule in the first place.
In general, you should assume that for any app that uses a device, that deleting the device is going to potentially corrupt the app. There is a warning about apps using devices when devices are removed, and that warning is there so that you know to go clean up that app first.
If you delete the device despite the warning, there can well be unexpected errors because of the app having lost its integrity. Sometimes these issues are benign, and sometimes they cause errors. The app has no way to know the device is being removed.
OK, so this is a bug / problem with Ecobee app. We will investigate.
Yes I agree about the potential to corrupt an app, and as such I typically remove all the rules that have devices associated with them prior to deleting the device, however in this case I simply forgot about that rule.