If the city decides to expropriate the land there is nothing that Johnny can do about it. Once the developer buys the rest of the block it won't be long before the city forces him out at a 'fair price' so that developement can begin.
Personally I think it's a shame to turn yet another part of the city into a haven of overpriced goods and restaurants with no character. If it goes their way, I imagine it will only be a matter of time before they move to St. Catherine street and start looking for ways to remove Foufounes which will certainly not fit with their new idea of an arts and entertainment district.