Am I remembering correctly that someone was talking about turning this exhibit into a salmon hatchery at one point?
Possibly, although the two old grottoes have essentially remained empty and unused for almost 20 years now. These 1962 bear pits certainly clash with the sleek, modern look of the brand-new aquarium entrance (built in 2014) literally a one or two minute walk away.
Have they torn down the old monkey cages and penguin pool where the zoo was or are those still standing?
Other than the polar bear complex the entire zoo is long gone and in fact there was a referendum in the 1990's whether to upgrade the facility or close it down for good and the public voted to shut things down. A barnyard zone remained open until 2011 but that is gone as well.
According to this zoo history the polar bear exhibit was already converted into a salmon hatchery: Vancouver History: Stanley Park Zoo Vancouver Blog Miss604 It clearly isn't a salmon hatchery now, so it must not have lasted long.