More than likely. As with the watch analogy, it won't be total extinction for "all-steel" but it will be a dwindling, niche market.
Polymers are cheaper to acquire and manipulate and more than likely their properties will continue to be honed and expanded to provide more and more qualities to the firearms made from them...
Corrosion resistance and weight are the two that spring to mind, but what else can industrial chemists get out of them?
Self-lubrication with super slick mating surfaces?
Recoil absorbtion through flex, rather than weight?
Hydrophilic grips to stop the grip slipping in a sweaty, adrenalised palm?
Funky transparent guns?
Quite exciting, really...
On top of that, I think that steel (already a strategic resource) will become harder to get, also...