I know that those with Full Control can override a checkout by another user (which causes the user's changes to be lost), but can the Full Control users also check in those publishing pages on a SharePoint 2010 (so changes by another user aren't lost)? Thanks.
Have you actually tried it yet?
Log in as a normal user. Edit a page. Save it, but don't check it in.
Log in as an admin, check the page in. See if the changes the user made are there.
My suspicions tell me that they will be there, as an administrator can always see the most recent version of a document, major or minor. The only thing is that the 'last modified by' field will be that of the administrator user.
There is an out of the box way of doing this -
Navigate to /_layouts/ManageCheckedOutFiles.aspx?List=ListGUID and take ownership for the Checked out files and check in