Events that have ended are still viewable for up to 28 days after they've ended.
From your calendar view, click on the event and open it. You can't make changes to the event after it's ended, but you can print standings, pairings, and other information as needed.
You can also view past rounds during the events you're currently running. When you view previously completed rounds, you'll see the round exactly as it would have appeared at that time. Pairings and standings won't reflect later rounds' information.