I think a bit of additional diagnosis would be needed. Is it still running automations? Can you ping it? I had for example my IP banned, which resulted in similar issues (has to be manually enabled in the http integration, I believe). And it rarely happens, but Raspberry Pis can also crash and become unresponsive. You could tell by nothing happening in the home anymore. Or maybe it somehow changed IP addresses? Does it have a static address or does the router do weird things with DHCP? Does http://homeassistant.lan:8123 work and then also stops working?