Its absolutely possible to have both a SaaS based control plane and continue functioning if the internet connection/control plane becomes unavailable for a period. There's presumably hardware on site anyway to forward requests to the servers which are doing access control, it wouldn't be difficult to have that hardware keep a local cache of the current configuration. Done that way you might find you can't make changes to who's authorised while the connection is unavailable, but you can still let people who were already authorised into their rooms.