You received emails that your CPanel server FAILED : tailwatchd and is not running follow these steps! Hope this helps.
1. You first need to check the tailwatchd logs for the reason as to why your tailwatchd has failed:
tail -f /usr/local/cpanel/logs/tailwatchd_log
2. Lets see what is handled by your tailwatched service.
3. Restart your CPanel service, this should restart tailwatchd.
service cpanel restart
4. Still receiving taildwatchd failed emails lets now force the tailwatchd update !
5. Last thing that will definitely get you to stop receiving emails and get things going again would be to reboot or restart your server completely.
I hope this helps you can always reach out to cpanel to help you get this issue resolved by providing the log.