The birth control dilemma has been reiterated and published from reputable sources and definitely put a fatal chink in the population's armor, but at the same time the population was already in decline of its own accord many decades beforehand, when you look at the actual historical data in its entirety.
The population began steeply declining in the 1970s when its primary source of growth -- captures and acquisitions of wild-caught bears -- became illegal, further impacted by the later restriction on overall imports. The last year where births outnumbered deaths (for the US population specifically, I'm not sure if this applies to North America overall) was 1987; They would have still died out whether or not the birth control incident had ever occurred, because polar bears have never, in their entire nearly 150-year history in North American zoos, reproduced self-sustainably. Ever. Even if we isolate earlier decades and begin the assessment at the absolute height of the population's reproductive success (relatively speaking) up until just prior to the usage of the birth control that caused reproductive issues, 1969/1975-2000, deaths still outnumber births.
There's little regional, historical, or statistical context in which to believe that the births of new young females or allowing rescues to breed will save the population in the US / potentially North America. Allowing new imports would, but only by virtue of increasing and maintaining numbers. I do hope my assumption is wrong, with consideration for the recent welfare and husbandry advancements in the last decade or so, but until that can prove out -- the existing data objectively speaks for itself.
