Your friend's husband can certainly lose his green card if USCIS determines that he in fact obtained it through fraud. Your friend can tell USCIS about the deceit and USCIS will then pursue the matter further with him. They will give him an opportunity to rebut the allegations but if he is not able to, then he will lose his green card and can be deported.
If your friend is the victim if marriage fraud, she should report the matter to USCIS or DHS. She should submit a detailed written statement and submit supporting evidence. USCIS or DHS can choose to investigate the matter further. You may want to consider retaining an attorney to assist you.
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It is the person's intent when the marriage is entered into which determines whether it is bona fide. Many marriages go downhill later on, and the two parties often say insulting things to each other.
Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.
Your friend can report the situation to the USCIS. Whether they choose to pursue the matter is up to them. It does sound like your friend needs to get out of the situation regardless of what happens to the spouse.