I really think the MLR cap was the biggest improvement Obamacare brought. It means keeping a genuinely expensive patient might mean your shareholders get to take home more money, so the incentive is "keep their business" rather than "treat them well enough that they can't successfully sue you for more than you'd have spent on them anyway."
Only if they are below the maximum premium profit-to-cost ratio (20/80), otherwise, they are going to have to refund the excess anyway, due to other provisions of the ACA.