When is it time for a great artist to retire? This delicate question hovers over the Metropolitan Opera’s revival of Verdi’s “Simon Boccanegra,” conducted by James Levine and starring Plácido Domingo in the title role.

Mr. Levine, 72, has long been struggling with health problems, including Parkinson’s disease. This year, the Met was poised to announce his retirement as music director when he was given a reprieve by his doctor, who thought an adjustment in his medication might better control Mr. Levine’s symptoms. This “Simon Boccanegra” is in essence a trial run.

It was hard to see how Friday’s performance could be determinative. Mr. Levine has championed this great but flawed Verdi opera, with its profound score but convoluted plot. He knows the music intimately and led a radiant, stirring, if sometimes uneven performance. His arm gestures and cues still seem loose and flailing. But by now the Met musicians must know what Mr. Levine is after, especially in a signature work like “Boccanegra.”