Unfortunately, the *.dat files are in some undocumented binary format, and the only tool I found for reading those lacks in features. Indeed, there is a bunch of *.dat files in the chatsync subdirectory of the Skype's profile, which preserve all messages along with all their edits or deletions. I found that curious and decided to take a closer look. In addition, Dominique made a remark that Skype does not really delete the messages that are marked as 'removed' in the chat window.

It turns out, if you obtain a person's Skype profile directory, you will be able to log in as him without the need to know the password.

Yesterday I happened to attend a discussion about the security and privacy of information stored locally in Skype and Thunderbird profiles. In other words - you would only recover 'removed' messages if you are running older version of Skype (or these messages were sent at the time you were using that older version). Either these versions stopped saving removed messages altogether, or they are doing it in a novel manner not recognized by the tool. Update from year 2017: The tool described in this post DOES NOT WORK with recent versions of Skype.

Dat files reader thunderbird