First, my apologies, deprecated might have been wrong choice of words… discontinued as @MyDayOfPlay correctly pointed out may be more suited. Refer to this article:
I personally enjoyed the Xenon boards they were very cost effective and a great board to use where simply put, only connectivity between end point device and a gateway was needed. You would have i.e. Multiple Xenon boards sending data (bouncing data off one another like stepping stones) to the gateway (Argon for WiFi and Boron for cellular) which would then in turn send data to the cloud. I was sad to see it discontinued, but understand their reasoning behind it.
You will now rely on BLE to make this sort of communication possible I assume, or an open source Blue Tooth mesh. Not sure how well it well it functions on Particle, I only used it in once my pre-Particle days. Had some success but not great. Xenon and Mesh will still be available for some time, however I will suggest not developing any new products based on the board and the technology as it has been discontinued.
Depending on your current needs, either one of the currently available boards will work well. Major factor for me to keep in mind is your prefered method of connectivity. If you want cellular, I go with Boron, if Wifi, you have to option of Photon or Argon.
So to answer your question in short; As far as I know Mesh will be lost soon and you will have to get similar functional using BLE in some way… at least for now
Hope this helps.