Likely not dead, unless you had an extraordinary event like a power surge that killed them. However, there’s just not enough detail in your post to do any significant diagnosis of the situation you’re experiencing. At the very least, I’d try a network refresh by unplugging the Sonos devices from power, then rebooting the router. Once the router comes up, plug the Sonos back in. 

If you happen to use a BRIDGE, unplug it from power, and run the Ethernet cable to a speaker instead. Wait a couple of minutes before checking the controller.

These are generic suggestions. If you’re interested in more useful help, more details about your Sonos system and exactly how they’re ‘not working’ would go a long way.