TFS gives you some powerful, but somewhat obscure, functionality for undoing users’ checkouts, deleting workspaces, and more. As a TFS admin, you run into cases where a user’s workspace has become irretrievable, whether due to the user no longer being available to the project or a loss of data on the part of the user. The command for this (covered in MSDN) is:

tf workspace /delete hisworkspace;DOMAIN\OtherUser

If you want something a little more granular, you can undo the lock on a checkout, but not lose the change. This command (also covered in MSDN) is:

tf lock /lock:none $/project/path/filetounlock.cs

If you truly want to undo a checkout, losing the change, you can use this command:

tf undo /workspace:OtherUserWorkspace;DOMAIN\OtherUser $/project/path/filetowhack.cs

If the developer has moved on, whether to another project, another company, or it was their gear that moved on and took their project with it, deleting the workspace will likely work best. You don’t have to worry about unlocking their files, and you don’t have to wander all over your source tree taking care of files individually.