Why did Opera Boston abruptly shut down. The company, it turns out, couldn’t recover from largely being abandoned by its biggest booster. It’s deficit had grown from about $250,000 in July to $500,000 by Christmas. With an expensive February production scheduled, “The Midsummer Marriage,’’ the board projected falling as much as $1 million in debt. That’s for an organization with a $2.5 million budget. Dropping the curtain on a an organization with a reputation for creative programming seemed the only solution.