It depends how you configure it, as you would be aware that ZD is managing the AP's and AP's are handling the wireless users or clients. Once you remove ZD from the network then AP loses contact with ZD however currently connected clients will remain connected depending on when AP reboots (configurable) to reconnect back to ZD. See the below URL and bigger the number, longer the user remain connected to AP and the network. New clients will be refused connection in scenarios where ZD is involved for authentication.
Let say in your scenario, you disconnect ZD from network for 20 mins and you have configured to make AP reboot auto after 30 mins then all connection with remain ok however new ones will be refused.
In WLAN tunnelled mode (not by default), all traffic passes thro ZD however in a normal /default mode a-k-a standard mode, it just handles the initial Management and control traffic, data traffic is switched to local AP network.