Should I buy an uninterruptible power supply for my router and modem?

If my neighborhood should suffer a large scale power outage, will Xfinity's network stay up and running?  Do you ever test this?

My DR plan is if the neighborhood goes down and takes the internet with it, then tether a cell phone.  There is a flaw in the plan: if EVERYBODY in the neighborhood does the same thing, then the network will be essentially useless.  However, if Xfinity's network is sufficiently resilient to where we can expect it to remain up and running, then it makes sense for me to buy a UPS for the modem and router (the computers are already on a UPS).

Do you ever test this?

Thank you

Jeff