Most music directors who last more than ten years with a single orchestra don’t wind up leaving under the happiest of circumstances (Seiji Ozawa in Boston and Charles Dutoit in Montreal come to mind,) but as Neeme Järvi prepares to depart the Detroit Symphony after 15 years at the helm, there seems to be no question that the DSO and its home city have been witness to one of the great musical partnerships of the era. “The Estonian-born conductor and this mid-American orchestra have evolved into a championship team. They have changed together, flowered together, triumphed together. Especially over the last half-dozen seasons, they have turned what once were highlights into a lofty new standard of excellence at Orchestra Hall.”