Fail bypass possible?

Is it possible to have a bypass of the phone system if my Asterisk server fails?

For instance, I would like my install to just split my line to allow extensions. If the server fails, I would like the call to still be able to make it to my phone. I know I’m a newb but would appreciate the reply.

I have registered my VoIP account to VoSP server through Asterisk and also use additional ATA to register directly to VoSP server. This way, when a call comes in, it rings both phones. If Asterisk fails for some unknown reasons, at least the phone attached to my ATA device configured to register to the VoSP server will still ring.

Does that still hold true if the ATA loses power? I have a similar need for a “fail bypass” FXS, but with the current POTS line into the house, even if the power is out, the phone still works. I’m guessing that’s not the case when using an ATA and the power to the house is out? Yes, I know I can use an UPS, but after an hour or two… (power grid sucks in my city).

Is it at all possible (supported or otherwise) to configure the POTS wiring such that there can be a single fail-safe FXS inline with or upstream from the FXO inbound line or ATA? It will solve all my 911 / mother-in-law watching the kids / wife complaining about “breaking” the phone / disaster recovery type of problems. I know how the wiring diagram would look, just wondering if anyone has tried it - doesn’t seem to be documented anywhere / not easy to locate a diagram or description of that configuration.