Deleting a campaign is safe. Here is exactly what it does.

Once you delete a campaign, you will no longer see it. Extrovert stops fetching new posts for the people in it, and it disappears from your campaign list.

Deleting a campaign does not erase your history with those people. If you later add the same person to another campaign, their history comes back with them. So you can safely delete a campaign you are done with and start fresh elsewhere, without losing your past activity.

Open the campaign's menu (the three-dots icon) and choose Delete campaign. You need permission to delete it, which means you are the campaign owner, or an admin or manager on the team.

Any comments you already posted stay live on the professional network. Deleting the campaign only stops future activity, it does not remove what was already published.

The confirmation message mentions prospects being removed. That means they leave this campaign, not that your history with them is erased.