As sad as it is to say, Boku no Hero Academia and Black Clover will likely be what keeps Weekly Shonen Jump afloat after it's last popular long running series ends (assuming it ends before either of these two). Considering more people are gradually waking up to those two series being awful, however, I doubt they'd be able to hold popularity for long and certainly won't surpass One Piece in sales. Only series that really has any chance of being Jump's next staple in terms of popularity, sales and quality is Hunter X Hunter, and Togashi's hiatuses makes it's publication schedule too inconsistent to bet all their hopes on.
Most likely, WSJ's popularity will collapse once OP ends. Only other alternative would be to bring the next new Dragon Ball spinoff from Shueisha's Dragon Room into their weekly lineup and milk it for all it's got. Either that or make Boruto it's cash cow.
