During our neighborhood National Night Out gathering two years ago we had a representative from the Fire Department recommend that anyone with young children or elderly residents consider keeping a land line. Not so much out of concern about the cellular networks being down, but because a landline gives an exact street address when 9-1-1 is called. This can be an issue if someone can call 9-1-1 but can't speak. Cellular, if working gives a vicinity and in densely populated areas like apartments, and condos, that can include dozens of units that have to be checked.
And this was an issue in Santa Rosa in 2017 in the days after the Tubbs Fire. Cellular towers burned, and it took days to bring in temporary cell towers. Landlines in the city were buried, and never stopped functioning.