No, if you power-off a Zigbee device with a dumb switch then it will be “offline” (as in unreachable, not available, which is unexpected and not a desired state in a Zigbee network), and more importantly, note that if they are Zigbee Router (ZR) devices and not Zigbee End Devices (ZED) then it is a really bad idea to power them off. Zigbee Router (ZR) devices always need to have power as they are part of the Zigbee network mesh infrastructure. See related discussion here → Stop Zigbee Mains powered device from being a router? (ZHA)