Hi, Mike,
Not to worry. Your movies are safe.
Go to your Movies folder (Go/Home/Movies). You will see your iMovie Theater.Theater folder in there. You won't be able to open it by double-clicking. However, Control-click on the Theater folder's icon and, from the drop down menu that appears, click on Show Package Contents. You will see in there several folders titled Archives. All of your movies are in those folders. You can play them there or copy (copy, not move) them to your desktop to store wherever you wish. I would suggest that you store them in a Finder folder on an external drive or on your internal drive. (You actually can move the movies out of the Archive folders by dragging them to your desktop, but I suggest copying them out of the Archives folders rather than moving them. That lets you keep your Theater folder intact.)
-- Rich