The OSC theatre is actually OmniMAX (even more immersive than IMAX). The OmniMAX projected images can fill nearly 90% of the surrounding dome theatre... absolutely worth saving!!
And while we're at it (speaking of film), if the Science Centre can't be saved... I'd repurpose the main building into a History of Cinema Museum, with tons of Canadian content such as celebrating the remarkable legacy of the National Film Board (incl. the 70 films of Norman McLaren) and the largest publicly attended film festival in the world (TIFF)...