Las Vegas Sands was once the envy of Wall Street. In fall 2007, with seemingly unlimited growth prospects in Macau, the most lucrative gambling market in the world, the company’s share price topped out at nearly $150. But then came the fall, a drop so fast and long that even in this era of suicidal reversals on Wall Street, Sands stands out. The company’s market value plummeted more than 90 percent.