What can you do when a teammate checks out a project file and then leaves on vacation without checking it in?
If you're using Subversion or the built-in version control system, you can break the lock your team member has - right from CaseComplete. To do this from the Project Browser, hold your SHIFT key down while clicking on the locked file with your right-mouse button. You'll see an option to break the lock.
Your teammate will need to re-apply the changes they made but you'll be able to check out the package or diagram and continue working with it.
What do you mean by 're-apply changes'?
CaseComplete's built-in project sharing control uses an exclusive checkout method, which restricts the ability to update a file to one person at a time. This is the "check out," which assigns the file to the person checking it out, and restricts the ability to make changes to (locks) the file for anyone else. When you break a lock, you're essentially removing the other person's ability to make changes and resetting the system, so someone else can check out the file and make changes.
Any changes the original person who checked out the file made will not get applied to the central (repository) copy for all to see, and that person will need to re-check out the file and duplicate any changes that were made.
You can read about other compatible version control systems here (https://casecomplete.zendesk.com/entries/234963).