If "stop the script running further" means you want to stop it from running YOUR event-handler code but not hiding the event's messages, you can do it the same way you can stop any other alias you make:

1. return
2. returnex
3. GOTO label_at_last_line_of_your_event_handler
4. Call My_alias without a parameter, but my_alias contains $$1
5. //echo -a $sha1 | echo -a invalid syntax stops your script