Your wiring supports what you’re asking for with no extra complexity requred. You need a Project Zephyr fan switch (ZigBee Fan Switch | Project Zephyr (Blue Series)) and a Blue switch to control the lights. If your network / hub is offline, everything works as normal.
You could accomplish the same with a canopy module (Project Cheryl, this thread) if it’s communicating with the switch/scene controller (Project Walt) via zigbee binding (aka if the network is down, the two devices still communicate directly with one another) , but I can’t think of any reason to do that when the basic setup covers your bases.