I ran into a few problems with the forum integration plugin that were fixed 2 years ago by an adjustment to the code. Rather foolishly I didn't check this, edited and overwrote cbsimpleboardtab.model.php directly on the server and broke things far worse. Is it possible to obtain just this file or extract it from the zip archives of the full CB package so I can revert to how it was originally? For now, I've had to remove the forum tab of my users profiles, I'd like to put it back to how it was before I started messing with the file.

Shall I take the deafening silence to be "No, you've messed it up now" then?

I think you should read the help us help. If you want help, then say which joomla version, which cb version you are on.