If a student graduated from a top school (i.e., MIT, Harvard, Stanford) and the university found out they cheated in past courses, would they be able to revoke the degree?

Yes. University and college degrees are based on not only your academic integrity, but on some Student Code of Conduct issues, as well. If a university or college discovered that a former student committed plagiarism or other types of academic fraud to “earn” that degree, it can be revoked.