This just happened to me. Whole game is gone…srsly?
Apart from what is already in that thread, this can happen if you install Call of Duty into your Battle.net application folder, or vice versa. The permissions get weird if you put it in C:\Program Files(x86)\Battle.net by default because Battle.net has to periodically clean out folders it installs on your PC so the client doesn’t get too large.
Have you tried anything to troubleshoot this so far? Where do you usually install Call of Duty on your PC?