If you want your script to fail and stop the automation, you can throw an error. Sorry I cannot format the text as code while on my phone.
throw "this is an error to cause the automation to fail"
You might also want to console.log() some key variables to give more info about why you want the automation to fail.
Another option is to have the script use output.set() to indicate the success of the script. Then use conditions to either take any additional actions of the script was successful, or have an email action if the script says it was unsuccessful. You will probably get the email from the automation email action sooner than the email notification about the failed automation. Of course it might be harder to identify the exact run in the history of it doesn’t fail.