The most innocuous thing will keep this from ever happening. The setting for the final battle. Marvel has a go-to in New York, NY. DC has Gotham City, Coast City, Central City, Star City, Metropolis, Bludhaven, blah blah blah. Just picking the right fake city for the denoument will cause fights that will shelve the stupid thing.
They should have been prepping for this all along alongside Marvel. Starting now just because is going to leave 'em sucking hind tit forever.