Most times, you'll know if even your own local gateway goes down but a lot of that has to do with how a network is set up.
Some folks have multiple internal devices like a wireless router connected to their own router which is then connected to their providers.
There is no way for the agent to know these things so to us, it's expected to work on a 'traditional' network which is usually the providers router/modem only.
That said, for companies that do have multiple internal gateways, we have a feature we can manually enable that tells the reports side where the local network ends and where the provider starts otherwise, those folks get reports of the LAN being down when it's actually the provider or vise versa.
Hard to have a tool that does it all automatically but we keep working on it :).