The Photon works fine right now with no Wi-Fi enabled. So if you’re only an XBee coordinator with no Wi-Fi, and of course, no Internet, all you need is [manual system mode] (https://docs.particle.io/reference/firmware/photon/#manual-mode).
Also, if you already have a Wi-Fi access point, even if it’s not connected to the Internet, that’s also no problem. The Photon can communicate with other devices like other Photons and laptops over Wi-Fi right now. There won’t be cloud access with no Internet, but they can communicate using low-level protocols like TCP and UDP, and also things like HTTP, without the cloud.
The issue you linked to is only in the case where the Photon is the access point for other Wi-Fi devices. That’s not yet fully supported. It’s sort of supported in the configuration mode ([SoftAP] (https://docs.particle.io/reference/firmware/photon/#softap-http-pages)), but not fully for general use yet.