Marriott seems to do OK with the situation at their JW resort in Summerlin, where the (smallish) casino is run by an outside license-holding company. IIRC, this was the arrangement when the resort opened as the Regent, and continued when Marriott re-flagged the property.

Maybe SPG could work out an "affiliation" type of arrangement with another Strip property (maybe TI, which is independently owned), as they once had with Caesars Palace.