I'm by no means knowledgeable about this stuff, so please correct me if I'm wrong.
Realistically, that isn’t happening anytime in the foreseeable future.
Even if BP considers the shares and the voting power completely and utterly worthless the other owners of Rosneft apparently don't and giving back the shares gives the other shareholders larger ownership of the company for free.
They just don’t want to be involved anymore.
Realistically if they keep their shares, they’ll get hounded by everyone to do said influencing or whatever, which would be really irritating for them I imagine. But maybe they will put them in a drawer somewhere in the basement and tell everyone to screw off. Who knows. They say they don’t know right now.
Either way, at minimum it's a gift of not crashing the price.