When I notice the license of my current repository on GitHub is invalid, what should I do?

Question

Say, if I found one of the packages in my project adopted GPL license, and I already had published my repository to GitHub as MIT, I immediately have to;

1. delete the whole repository.
2. change the license to GPL.
3. remove the dependency to maintain MIT license.
4. No way. I'll be sued for it someday.

Which would be possible choices?

EDIT:

I didn't know the example above is okay. So let me change the assumption.

If I found one of my JS, CSS, HTML or other stuff had been brought from MIT licensed source and I had never put the copyright notice in the file, I have to;

1. delete the whole repository.
2. remove the file or substitute another file for it.
3. No way.

Answer 1

If you find out that you are not fulfilling the obligations that a third-party license puts on you, then you should correct that as soon as possible.

If copyright and/or license information is missing or incorrect, you should update those files so that they contain the correct copyright and license information.

If a third-party dependency, which is not copied into your repository, changes its license to one that is incompatible to your license, then you should first try to pin that dependency to the last (tested) version before the license change.
After that, you can take your time to consider if you can replace that dependency with something that does have a compatible license or if you want to change the license on your project (which can only be done with explicit approval of all contributors).

In any case, these actions show that you are serious about copyright licenses and that you don't try to take advantage of someone's code. Should they try to sue anyway, that will probably be looked upon favorably by the courts.