So...basically your critique is that you don't think I'm right, but you don't really know?
It's absolutely right that the city would find it difficult to prevent demolition of buildings, at least without the City of Toronto Act. That's not necessary, though. The city merely has to control which sites can be redeveloped. Sure, you can tear down a building, but why would you if you can't build anything to replace it? The city can zone any part of the city any way it wants. It also has to approve every change in zoning, which is required for virtually every large development. An official plan amendment preventing the demolition of buildings in neighbourhoods where a large number of undeveloped lots exist is entirely within the realm of the city's power, especially after the new City of Toronto Act.
AP, the city can prevent redevelopment on virtually any site, unless they're planning to put up a building that's exactly the same size as the one that they're tearing down. The first line of my post was that the city cannot force development on any lot, so obviously it wouldn't inevitably result in development of empty lots. However, if there's a neighbourhood with significant demand for development, and empty lots were the only lots where it's allowed, what do you think would likely happen? I was also not talking about these buildings in particular. I was simply responding to the endlessly repeated point that the city somehow has no power to regulate development on private property.
I'm not even necessarily advocating such a policy, and I think it's probably too interventionist in much of the city. I'm simply trying to dispel this myth that development is somehow inevitable and the city has no power to control it.