Before a Campaign Automation is published, nodes (actions, triggers, and timers) can be safely added and deleted as needed. However, once a Campaign Automation has been published, any edits made to it will affect the participants currently running through it.
Deleting a node in a live Campaign Automation is not considered a best practice. Learn more about scenarios of editing a live Campaign Automation and how to safely do so here.
Participant Status
Your participants currently in that node will be stopped. So if you delete a node with 4 participants in it, after deleting that node the Participants tab will show a status of Stopped for those 4 participants. (The Stopped status will not have an extra explanation that it was due to a deleted node.)
If you want to see how many participants are in the node you're planning to delete, select the Statistics tab. The nodes in your automation are shown with information on how many participants have completed, are active, or have failed in each node. Check the specific node you plan to delete to see if any participants are active. In the example below, the Date Timer shows no participants being active.
Deleting the Node
You will see a warning before deleting a node.
If you're comfortable proceeding, select the Delete Anyway button and that node will be deleted.
Troubleshooting
Deleted nodes are not visible in Mongo so if you believe that a Campaign Automation is having issues due to a deleted node, you should check in the STP CA audit history. That will pull up all changes made to the CA and show if a node was removed.