was there anything as error message in the SolarWinds log files? That would help us to understand the root cause.
Current alerting doesn't have something like "heartbeat" alerts. But, you may may for example write a fake alert (just configure any kind of alert that will be triggered all the time, like PollingEngines.StartTime is >= 0, set the same condition to reset and set the interval for 1 or more minutes) and as the alert/trigger action you may set an execution of powershell or vb script or app that will send a heardbeat into your monitoring service. you may also uncheck "alert sharing" so this alert is not propagated to the other product.
that was what we were thinking as well but the problem is; someone might have missed this 'heartbeat' alerts. what i was thinking is to send an email every few hours through alerts as to inform that alerts module are up. when this got more, i believe ppl will start to ignore. i was thinking if there is anyway if it is possible to inform only when alerts went down?