When a project has ended and a campaign is no longer needed you can easily archive it. Archived campaigns are not visible to agents, but managers will always have an access to it. This way you will not lose any data and you will always have an access to reports and analytics from that campaign. Additionally an archived campaign is not counted into campaigns limit.
To archive a campaign you need to go into campaign's settings and in the "Basic" tab click on a red button "Archive". The button will be only active when a campaign has an active script.