WD Passport Doesn't show up anymore

It is possible the drive may have gotten corrupted, especially if you disconnected the drive without safely removing it first.  The fact that it still shows up in Disk Utility is an indication of that.  You might try looking for partition recovery software to see if that will restore the files.  Also, if you manually copied and pasted anything to the drive while it was connected as a TM backup drive, the drive could have become hidden.  You will have to contact Apple about that.