What will happen to leads currently in flow steps if you deactivate a trigger campaign?
If you deactivate a trigger campaign, all leads that are currently in the flow will still be processed. Deactivating a trigger campaign will only prevent any new leads from qualifying for the campaign and going through the flow steps.
To stop people from continuing through the campaign flow steps, you have 2 options:
Remove people from flow steps. (Recommended option) Note: You may want to add that flow step after every flow step, to target all areas where people may still be in and processing.
Delete all flow steps. As people complete any flow step, they will no longer have a next option.