I'm almost 100% sure she's not going to change her last name.
Maria Sharapova has become a brand. I'm almost 100% certain she'll keep it that way—even if she wanted to change. There was a survey on Yahoo! I read last week about women keeping their maiden name. Usually women who are independently successful in their respective careers keep their maiden name. I think it's more common in the Western world for women to take their husband's surnames once they are married, since my mother kept her maiden name.