Where to store critical data in power outage situation on ESP8266
If you worry about the maximum number of write cycles, you could write the data to an SD card or some FRAM connected to the ESP8266, or you could send the data to a (web) server (if you have access to one) using WiFi. The server can then store the data.
If you really care about the data, you could do both. Having a backup is the only protection against catastrophic failure.