Your clients who stay on their AP should have local connectivity (until the AP reboots after X min recovery settting period).
Open Auth or WPA-PSK clients may be able to roam, but not 802.1x, WISPr, or Guest Access WLAN clients, who need
the ZD for re-auth.
See also "Autonomous WLAN", designed for use if/when ZD connection is lost, in the ZD User Guide.