Re: how to get alert or mail when task fails in qlikview?
In many cases, that seems perfectly logical to me. A service that is responsible for sending notifications and that goes down is as a result unable to send notifications or anything else.
There is a difference between
sending notifications about reload failures (the second part of your question). Than can be dealt with using the QMC settings for messaging.
sending notifications about crashed/inactive QlikView services (the first part of your question). In the Power Tools 1.2 for QlikView package, there is a tool that checks on QlikView service activity (for all of them) and sends a message when one or more of them prove to be unresponsive. Easy to set up.