FWIIW: We experienced an outage last Friday. Fortunately, most of it was after business hours. A few of observations:
1. I get an email if the queue holds more than a few emails, I can then notify support and their response has been good.
2. Typically, what few ASG outages we have had were caused by failure to deliver the mail from ASG to our Exchange server and the mail was available in the archive.
3. Because we have had other outage causes besides ASG, I wrote a script running in a 24x7 system, that sends myself and another person an email every hour (via a personal email account hosted elsewhere). This, along with the queue alerts, notify me if mail has stopped (no, I don't monitor 24x7).
Although I don't consider any failure acceptable, it happens and I don't want to find out about it from the users. I hope that Comodo fixes these outages and would prefer if they were more proactive about alerting us when an outage happens.