The dashboard continues to display the last telemetry from the Pi. In the case where I rebooted and connection was not re-established, you could not tell from the dashboard (except by trying to reboot from the dashboard and observing that the Pi ignored the command). Every so often the dashboard needs to check the connection to the Pi for a ‘heartbeat’ and display that the connection is present or not.
If there is no connection to the Pi you should see at the top of the page it says Offline. If not try refreshing the page to see if it updates.
Going off of Adam, if the little Pi icon in the left panel is red, then the Pi is online. If it’s grayed out then the Pi is not online…does this help?