They all continue to work in dumb mode, once a Shelly is installed and the hardwired switch is wired to Shellies SW input and Shellies O is wired to a lamp.
In any case, no matter if WIFI is available or not, the hardwied switch will still turn the light on and off.
Further it can be configured to reinitialize WIFI connection whenever it was lost, without influence to current switching state.
Further a back-up WIFI can be configured such that the Shelly would have a fallback opportunity.
Of course if a installed Shelly sends on/off commands via WIFI to a remote Shelly, this won't work without WIFI.