Actually when you are using webhooks, Unbounce only knows and shows what the webhook returns as a response.
If the webhook passes the form’s data successfully the API usually returns a 200 response (successful execution). This is what Unbounce displays.
If the webhook submission is unsuccessful, the API similarly returns an “error” response. Only this time it’s not a 200 but some other response, depending on how these responses are setup on the API side.
There is no way for Unbounce to know whether the API is functioning unless your webhook reports back.
So going back to your original question… You should adjust your webhook to fire off an email each time the response is anything other than 200.