Upvote:4
The simple answer is, "probably back to Russia". I would be extremely surprised if you could find any currency exchange or bank in the USA that will accept Russian currency. The only exception could be in some heavily Russian-speaking areas, for example, Brighton Beach in New York, yet even that is questionable.
Your friend's best bet is to hold on to it until his/her next trip to Russia. I still have some Russian currency from my last trip to Russia about 3 years ago.