A back up UPS goes a long way to solving any power interruptions
We have one… but it does not cover hours/days… it give me 30 mins I think… enough time to save my work and close down the computer.
Back in UK my firm had a UPS/battery system which would last for some days… but it took up a lot of space… 
You have to remember that the cabinet that you connect back to is likely fed from the same mains supply as you are - they do have batteries/UPS’s but typically only enough capacity for a few hours.
Yep, we bought one suitable for our personal needs to safeguard my computer work… anything else (much longer time) … was prohibitively expensive…
Mobile phone coverage in France is excellent. Orange themselves have realised that there is no longer a need for a traditional fixed line so are phasing them out so a non VOIP backup will soon not be an option. Every VOIP phone number that I’ve had in France had a geographical number, the last one I had started 05 because it was in the Poitou Charente, before that, north of Paris, it was 03.
Sadly, as I have said… mobile phone coverage is NOT excellent in all parts of France.
When folk visit here (from wherever) they can often be seen wandering around the village, with their mobile device… searching for a decent connection… 
They look so forlorn… 