Regular badges will not be revoked except in very special circumstances.
How do "badges" work?
> Regular badges, however, once earned, are yours to keep. Even if the criteria by which you earned a badge have changed (the post was deleted, you got downvoted, etc.) you get to keep your badge. If you qualify for the same badge again (another post earns you a post-related badge, for example), you won't be penalized either (source).
Regular in this context is opposed to tag badges that come with privileges (e.g. a gold tag badge gives you the right to unilaterally close a question as a duplicate of another question with that tag).