Getting Bonfils/Lowenstein approved for landmark listing should be a slam-dunk -- the association with Helen Bonfils alone would be enough to cinch it as far as I can tell. Not only that, but it's already been evaluated as being eligible for a listing on the National Register of Historic Places, and extensive research on the building and the history of its productions is found in the files of the Colorado Historical Society. Lowenstein's near-encyclopedic collection of programs is in the Western History Collection of the Denver Public Library, and they could also be used to help make the case.
Only a public hearing will get the preservation issue into the political world, where Mayor John Hickenlooper and city council would be forced to take a stand one way or another. And that's the only hope we have of averting yet another architectural, cultural and historic tragedy. I want to be optimistic here, but Denver does have a sad and longstanding tradition of erasing its architectural assets.