Have you logged in as the user that has left, and that's where you're testing? Sounds like the Signature files aren't there anymore, or you're using a different profile.
The signature files are stored in:
C:\Documents and Settings\<username>\Application Data\Microsoft\Signatures
or
c:\Users\<username>\AppData\Roaming\Microsoft\Signatures
If the profile of the user that has left is still accessible, you can just copy this folder to the same location in another profile. You can also check this folder and make sure the logo's, signature doc text etc.. are in there.