Could they also have become extinct, hiding their genes in a population of Grizzly or Kodiak bears, for the “polar bear” genes to be selected upon again after t

Could they also have become extinct, hiding their genes in a population of Grizzly or Kodiak bears, for the “polar bear” genes to be selected upon again after that close escape? https://en.wikipedia.org/wiki/Grizzly–polar_bear_hybrid https://en.wikipedia.org/wiki/Grizzly–polar_bear_hybrid: “Genetic analysis has revealed multiple instances of introgressive hybridization between bear species, including introgression of polar bear DNA into brown bears during the Pleistocene ("grizzly bear" is a local common name for Ursus arctos whereas "brown bear" is used internationally and in science to refer to the species as a whole)“