I always feel sorry for anyone experiment failure.  It, it happens. Often an electronics failure will be soon after purchase, or following many years of service so it is very unfortunate when it happens after only a few years. 
That said, can you tell me any other manufacturer that gives any discount to customers in this situation? Most will simply say “hard luck” rather than “hard luck but here’s a hefty discount against the replacement cost”. 
If you’re seriously “ending your relationship” do you mean you’re getting rid of all Sonos gear? That sounds like a far more expensive route to take. 

If you aren't happy with the one-year warranty there are extended warranties available. I usually pick one up for Sonos I am gifting,  not for Sonos I am keeping though.

The Sonos 30% after warranty discount is a better deal than any other audio gear seller has offered me.

One thing I do that i think has contributed to the long life of my Sonos is using a QUALITY surge suppressor on each of them.

If you are selling your Sonos, the broken Sub will also bring some money on the used parts-only market.

The same thing happened to my Sonos Sub V3 yesterday. Contacted support and explained situation along with a video of a strange sound coming from the Sub. Awaiting a response.