If you want to branch a call based on the device status of a single extension, you can do so using dynroutes and this method: Using Dynamic Routes to branch call flow based on extension state
Using dynroutes you can check the extension hint for the value of UNAVAILABLE and branch the call that way. You can probably string multiple conditions as part of the expression using and/or, but I don’t recall ever doing that so you’ll have to google it.
Alternatively, if there is an API you can call somewhere that will tell you if the office is occupied, you could use that with dynroutes as well.