Yes. You can always delete a campaign from your timeline under "Overview". Or essentially, this is only de-activating the campaign, as the saved investment scenario that you previously saved to "Activities" and then activated, to have it go into the timeline, will not be deleted by this action.
This means that you can potentially delete any campaign from the timeline, and then re-activate it if needed, from the original saved investment plan, under "Activities".
To delete/de-activate a campaign from the timeline, you simply click the menu just to the right of the campaign name (the three little dots), and then select "Delete":
