Disable "double click on a tab preview to open in a new window"
 

This could be a hidden preference (i.e. defaults write ...) . I do it by mistake every day (don't ask me how). I have never once done it deliberately. Else a way to redock it (or an undo cmd-Z) would make me happy :)

A lot of people do this on laptop trackpads and we may add a preference or something in the future.

You can re-dock it just isn't as easy as it could be. Open the tab drawer and drag the tab back into the original window. Don't drag the favicon from the Address Field or Title Bar though as that will reload the page.

How about making the action undo-able? ;-)