I doubt many are gonna walk away. Most of initial buyers bought when prices were 650-800psf anyways. And people who bought recently at $1200 probably know prices are not gonna climb higher for awhile at least, so can most likely afford it. Also, from what I've heard, buyers at todays price may possibly be international businessmen, possibly from New York, London, Hong Kong, or Mumbai for example where prices are much much higher. 5 star luxury in Toronto is a bargain to them.
It would have to be a very very dire situation for these people to walk away from there 250K+ deposits, especially with mortgage rates so low.
Lastly, this is not Vancouver where the Ritz was selling at 2300psf, or Dubai where the trump was selling at 3000psf. Heck a regular, nothing special tiny apartment in manhatten is 1000 psf, nevermind luxury. People who can afford these units can afford to travel and know they are getting a deal.
That being said, there might be the odd one, two, or few that were really stretching it to buy ultra luxury, and got affected by the downturn enough to not be able to afford it, who knows, until it happens.