And here's the problem with many Torontonians! Why do you say there's not a chance? I'm living in Calgary right now and you would be surprised at how 'powerful' (in the corporate, office space absorption sense) the core is. Even the downtown mall of Calgary is huge with the Holt Renfrew being bigger than Toronto's on Bloor.
Don't dismiss other places' rise and to me, that's both Calgary and Missisauga (yes, to a degree this city is benefitting quite a bit at the expense of Toronto!).
In Toronto, Bay Street will always be that 'top' street, which symbolizes the financial sector of Toronto, and additionally, from what I know, it seems to have the largest number of skyscrapers in Canada (i.e. no other single street has more skyscrapers that Bay Street).
I am actually curious to see what % of Canada's top 500, 1000 or 1500 corporations are located in downtown Toronto vs downtown Calgary. I have a feeling it's the latter that may have more. From a physical/visual perspective, Calgary has more office towers that are 30 stories or more than Toronto, meaning it has the most in Canada. If you don't believe me, please check the lists online (I'm not going to bother looking it up and posting them here).
And no, I'm not anti-Toronto! I love Toronto and hence my presence on UrbanToronto!

In fact, I'm planning to move to Toronto early next year.
But the reality of Toronto must be stated! Its office market (in the 416) and its public transit are less than stellar from my perspective.
Taal, I completely agree with everything you've said about the office market (the core is OK at best, the outer 416 sucks and the 905 has seen benefitted a little too much at Toronto's expense).
I also agree with the 'musical chairs' of companies downtown comment - there seems to be little new growth in the core's office market; so far it seems more like companies moving from one of the older buildings to one of the newer ones.....(Telus being the exception).