I too have a freeze alarm which has saved my butt more than once over the years. I had the same concerns as you when I ditched Metrocast cable last year and went with internet TV (Roku
)
I chose to keep my Fairpoint land line just so the Freeze Alarm would have a
reliable way to call me in the event of an outage. Search the forums and you will find many who agree that the most reliable utility in your home is the POTS line ( Plain Old Telephone Service). Internet phone service is not very reliable and I certainly wouldn't trust it to protect my home from major damage!. If you are the gambling type you could get a Computer UPS that you could plug all your telephone gear into to help in the event of a power outage. Don't plug your Freeze alarm in to the UPS as it has a battery (9v) back up. By doing it this way you will get a call when the power goes out and the freeze alarm is on its own battery power, the UPS should keep the phone running for a while. In this scenario at least you will / should get one notification that the power has failed, eventually the UPS will die but you will be aware to check it every so often.
YMMV Good Luck, counting the days until the boat can go back in the water.
Charlie T