What will happen if my sister gets a divorce from a green card holder?

Last year my sister got married to a guy from outside the country. Next month will make it a year that they have been married. I believe the marriages is a sham. I believe he married her to only a receive the green card, and she's being fooled! I speak to her regularly and she says she's starting to believe me; that he didn't marry her for love. Btw, he refuses to tell his family and mine that they married. I'm the only one that knows. And, they have never consummated the marriage! If she divorces him, can he still be deported?