It was only four years ago that the St. Louis Symphony Orchestra faced the very real prospect of bankruptcy, with the best-case scenario seeming to be a drastic cutback in the ensemble’s artistic quality and national profile. And yet, as the SLSO prepares for its 125th season this fall, it has raised $80 million for its endowment, appointed a new high-profile music director (David Robertson) to replace the late Hans Vonk, and generally sent out word that it is as viable an organization as any in the U.S.