git push origin :master when you mean
git push origin master. Instead of coping your master branch's local changes to the remote repository you delete the remote repository's master branch. You can't undo this mistake. My initial reaction to the fact that I just deleted the company's source code was not a comfortable one. What I soon found out, however, was that you can just push again your master branch to return it to the remote repository. I am not sure this is the correct fix but it did seem to work.
Update: Here are my git notes at github.com