There will always be electricity available, but it'll come at a cost. I expect businesses running duplicate capacity for redundancy (ie AWS) to spike in price first.
The French grid is mostly powered by nuclear and has been for years. I don't expect much of a problem there even with rising gas prices. The total energy consumption graphs online that show a significant amount of fossil fuels seem to also include other types of energy consumption such as heating.
I wouldn't worry about this for now. Make sure your offsite backups are working and prepare a plan for migration to any other host if you're worried, but with OVH I'd be more worried about the data center catching on fire than electricity being cut for more than a maintenance window.