A well-designed home automation system will still work with manual controls and/or if the system is offline.

I have smart devices everywhere yet I can still adjust the thermostat manually, turn on lights using a normal switch, set the house alarm using the keypad etc. However, I also have a 'Night' scene in Home Assistant which sets my alarm to night mode, turns off all the lights in the house and sets the thermostat to night temperature all with a single tap and all over the local network.