It sounds like BP will be selling their stake to another party. So, BP will receive cash from the other party in exchange for shares in Rosneft. Whether the sale is a smart move for BP ultimately depends on two things: 1) the sale price 2) the expected future cash flows from their stake if they didn't sell.

My guess is that this will be a highly negative EV trade for BP because: 1) they're unloading a huge stake which will result in a depressed share price due to supply/demand imbalance AND 2) share price is probably already undervalued due to the fearful climate.