Plushenko could have left Mishin, as long as they had their finances in order, since often coaches didn't charge up front, but took a percentage if earnings. Plushenko could have afforded a financial divorce starting from his late teens, had he wanted one.
If Plushenko was in it for the money after he had provided for his family, he would have stayed married to his first wife, whose father was a bazillionaire. He could have stayed in politics, gone into business, made a fortune as a front man, and left skating behind instead of actively producing shows, starting a school, and doing the work. I never got the feeling he was in it for the money for himself so much: if anything, his comebacks were for the medals for him and money for Mishin's rink. St. Petersburg was heading towards being a skating ghost town for a while. He could have made more money in other skating ways.