Of course not all, depends, but I worked in a telco; and pretty much yes. Without datacenter, no cell phones (or trunking in the case I know) so no ambulance, no police, no firefighters (or a very delayed version)

We had batteries and 2 generators, and once we were minutes from blackout, as the primary generator failed, and the secondary was not dimensioned to cope with the load of AA of a 45 celsius day