Developers are required to take surety bonds to satisfy Tarion requirements to protect deposits, not the project construction.
There is nothing to say that after he fired the original CM, Mizrahi could not have setup a contracting company to complete the work, and get it bonded. It sounds like this isn't the case though.
What has happened is that the new owner (the receiver, essentially) has selected a new owner's representative (Knightsbridge) to oversee the developer/construction manager (Mizrahi). Don't forget this project has gone into receivership not bankruptcy, it is a bit different. Firstly it is not voluntary, so this was sprung on Mizrahi by his secured creditors. Secondly, in receivership, the debts are not wiped out at all.
The fact they are continuing construction and even injected money is a good sign that the receiver believes continuing construction is the best way to maximize paying back the secured debt. A sale is always possible, but who would buy a half sold building that requires hundreds of millions of dollars to complete construction?