I am streaming , how can I play music when provider goes down.

I just have a fanless computer  running Roon,qobuz and separate dac 

The Qobuz app (Mac, PC, or mobile) has a built-in facility to download music that be played offline.

https://help.qobuz.com/en/articles/10133-is-it-possible-to-listen-to-music-without-internet-connection

To use it, you need to run the Qobuz app as your music player instead of Roon. Music files that you download (Qobuz uses the term "import") are encrypted and can only be played by the Qobuz app.

If you prefer the Roon user interface, perhaps you could switch over to the Qobuz app only while your internet connection is down. You can pre-download (import) enough music on Qobuz to get you through periods when you have no internet.

Get an Eversolo DMP-A6 and install a 2TB m.2 drive internally, then copy your music onto that. No network required. Someone else mentioned Blusound, get a Node, and an M.2 drive in an external USB enclosure, ditto. 

I think some people confuse "service interuption" vs "network failure". The "Internet is down!" is a generic term for "things aren’t working". In the case of server/streamer/player, music files sitting on the server are not dependent on ISP functionality. As long as your network is healthy everything in your intranet should be just fine. No need to bring out the ukulele.

If things are not working and you are musically compromised, you can introduce a new topic to the group for discussion like: "Should birthdays be celebrated ON your birthday, and not another day that’s more convenient?" It could be quite engaging?

I'm a network engineer/architect by profession,  just wanted to get that out of the way.

The easiest answer to your question,  your internet provider connects through your WAN which is external to your local network,  LAN. Even if your WAN is down you should still have access to your local resources, ( music server). Unless your software needs to see an external WAN heartbeat,  you should be able to access your locally stored music..

Ok thank you gumbedamit I have 1Terabyte of Flac files on my Solid state 

drive  how could I access this to play ,and how can I pick out the music i want to play if say my ptovider Spectrum is down ?  
how can I choose ,access of the music ?

I am used to pick everything on my iPad .if I bought say a Innuous with a hard drive 

and streaming can I then maybe do this easier then my purpose built , computer ?

thanks all for the assistance 🙏👍