DETROIT – When Johnathan Shearrod gazes at Van Gogh’s “Self Portrait,” Bruegel the Elder’s “Wedding Dance” or any of the other treasures at the Detroit Institute of Arts, he can’t help but fear for their future. If Detroit falls into bankruptcy, those masterpieces and other prized artworks could go on the auction block to help satisfy the city’s staggering debts. Though the auctions would raise much-needed cash, they would also strip the city of its cultural riches, including paintings by Rivera, Renoir and Matisse, and maybe even zoo animals and historic automobiles. “The art here is just as important as...