The company that manages the largest group of downtown Las Vegas casinos is leaving Glitter Gulch, a move that adds even more uncertainty to an already struggling gambling market. The Las Vegas-based Navegante Group on Thursday announced it would part ways with Tamares Group of Vaduz, Liechtenstein. That leaves Tamares, the largest private landowner downtown, to find new management for the Plaza, Las Vegas Club, Western and Gold Spike casinos, a collection that includes more than 1,600 hotel rooms, nearly 2,400 slot machines, 51 table games and employs about 1,600 people.