[j_s]

  > It's possible to be careful about rebasing code, say by duplicating the master 
  > branch and rebasing your code on that new version to see if you accidentally 
  > destroy the world before trying to rebase within the actual master.

Is it possible to ask 'What would you do if I rebased' without a test branch?

[threedaymonk]

You can always do "git rebase --abort" if you're stuck in the middle of a rebase, or, if you've rebased and don't like it, "git reflog" to find the previous state followed by "git reset --hard <hash>" to get back to where you were.