Sports leagues are desperate for a safe way to start playing games again. Las Vegas has tens of thousands of empty hotel rooms and a tourism-based economy that has been wracked by the coronavirus pandemic. Could they help solve each other’s problems? MGM Resorts International, the company that has ownership stakes in more than a dozen hotel-casinos in Las Vegas, has pitched several sports leagues, including the N.B.A., W.N.B.A., N.H.L. and M.L.S., on an audacious proposal to house their athletes and necessary support staff to hold their seasons on a quarantined block on the Las Vegas Strip, according to multiple people familiar with the discussions who spoke on condition of anonymity because they were not authorized to comment publicly.