Will the thermostat work if connection to the cloud is lost? - User Guide - RDS110

Yes, the thermostat (hardware unit) works with or without the network connection:

• If there is network connection to the cloud and you’ve also set your scheduler, the thermostat works following your scheduler. Your temporary change of the temperature setpoint only takes effect during the current scheduled mode.
• If there is network connection but you haven’t set a scheduler, the thermostat works following the default scheduler set by the system). For more information about the default scheduler, see Setting schedules.
• If there is no network connection or valid time, the thermostat cannot get scheduler information from the Cloud. It always works under the “Comfort” mode.