The landline option I had previously was serviced by my cable company. If my internet was out, so was my landline, despite it not being VOIP. At my previous residence, it was serviced by the local phone company, and ran through a multiplexing box which plugged into my house power. Both that option and my cable modem have battery backups which continue to function in a power outage, but once that's gone, no more service.

That leaves only VOIP provider outages as a concern, and I've yet to experience one of those in a few years.