So many stories converged on Sunday's season-ending concert by Accordo -- the flexible, five-member string ensemble comprising principals of the Saint Paul Chamber Orchestra and the Minnesota Orchestra -- that the group's all-Beethoven program, though vividly played, was in danger of neglect.

Begin with the venue: Minneapolis' troubled Southern Theater. Accordo, founded in 2009, was born out of conversations between SPCO concertmaster Steven Copes and the Southern's recently departed music curator, Kate Nordstrum -- a presenter of rare initiative, and a casualty of the theater's fiscal crisis. Because the group has been so closely tied to the space, the ills of the latter raise doubts about the survival of the former.

In an e-mail exchange last week, Copes sounded guarded. "All intentions are to have a season," he wrote, referring to 2011-12. "We have programs and dates settled on. But these of course might change, depending on what happens." On Sunday, however, Nordstrum expressed confidence that Accordo would be back in the fall, though probably not at the Southern.

Copes has been out of the country since mid-May, depriving Accordo of its ringleader at a critical moment. Two other ensemble members were also unavailable for this concert: cellist Ronald Thomas, who's been on medical leave all season, and violist Maiya Papach. This left only violinist Ruggero Allifranchini and cellist Anthony Ross (who played in every piece Sunday, and whose spoken introductions added much to the evening) to represent Accordo's "brand." But guest pianist Rieko Aizawa and violinist Erin Keefe contributed strongly, as did SPCO principal viola Sabina Thatcher.

Like Copes, Aizawa and Keefe are products of New York's Juilliard School and Philadelphia's Curtis Institute. Aizawa, whose playing I've admired for years, was the last pupil of the legendary Mieczyslaw Horszowski, who died just shy of his 101st birthday. Keefe is an artist-member of the Chamber Music Society of Lincoln Center; she's recently served as guest concertmaster of the Minnesota Orchestra, which is to say that, like Allifranchini, she's a candidate for that long-vacant position. (No rivalry was detectable Sunday.)

But enough background. The evening belonged, finally, to Beethoven. The pièce de résistance was his Op. 95 String Quartet ("Serioso"), which, after 20 minutes of unmitigated intensity, ends with 30 seconds of seeming elation. Should this ending, so far removed from what precedes it, be taken seriously? Sunday's performance offered no answer, but made the question unavoidable.