I imagine that construction costs in such a remote area are astronomical. Under the Soviet system, the buildings were simply built regardless of cost because the economy was centralized. Now, most Norilsk residents probably don't want to shoulder the costs of construction there. After all, the salaries are high for unskilled Russian labor but still not high (2,500 USD/year in 2011 [0]).

Apparently, apartments are dirt cheap too, and other prices are quite high [0]. So maybe Norilsk residents don't have the disposable income to replace the blocks even if they would like to.

[0]http://siberianwonders.com/2011/03/norilsk-nickel-siberian-c...