The way our company's branches are networked is via a sisco broadband router and wired 8-16 way switch at each location. Its rare more than 16 ways is needed (one for each till, WLAN access points (usually 3), store server and workstation(s), kronos machine.
Each item has its own unique company IP address. And the router is linked directly to head office, where there are numerous servers. At any time, IT can dial in and resolve problems with tills, server and workstations remotely.
The clear problem, IMO, is when the broadband connection fails and the router needs rebooting, invariably at night when the premises are unoccupied. I am aware such routers as ours can self-reboot, but ours arent set up to do this (on the router it states "bt managed service")
Another problem would appear during power outages at the head office server rooms (does happen from time to time), since no alarm signals could be transmitted during this time. And they dont have backup power - there was a scheduled outage today, so they sent a message to all stores advising to send orders early.
The power supply in my store at least is secure, we havent had an outage since we opened nearly a year ago. But the router is not on a UPS.
TBH, I'm very surprised, given the complexity and apparent robustness of the network, that we dont have IP phones! Maybe the next step in our reliance on the network (or maybe they dont trust it enough for such a vital service as phones)