OK, I have no idea what happened, but I'll try to assist. The contact list is a file named abook.sqlite and the collected contact list is a file named history.sqlite. You could check in your profile folder to see if there is another profile that contains these files. that is, sometimes thunderbird makes a backup profile. You can check this by - clicking help>troubleshootinginformation - scroll down to 'profile folder' and click 'open folder' - click back one folder to the Profiles folder and then click to see if there is another profile. - if so, check for those files to see if they might have been recently used. if they look reasonable then exit thunderbird and copy and paste these files into your primary profile.

This may not work, but I am assuming that the file hasn't disappeared.