If my system control panel loses Wi-Fi can I still control the system from the app

Yes, IF your system control panel has a cellular communicator installed and working properly.

Conversely, if your system's cellular connection fails, you can still control the system through its Wi-Fi connection, provided the Wi-Fi is working and connected to the internet.

In either case, the Wi-Fi or cellular connection should be restored as soon as possible to maintain the desired redundancy.