They don't right now, I can't run any reasonable models above a $20 billion BO if I was BP and had to sell the deal to shareholders and the board. Assuming label expansion, generics case resolved, etc...
I think they'd buy it for 12-13B no problem, would they go 20 or above? Maybe in 6-12 months depending on label details, sales uptick, patent strength and other factor, I think they would