There are already a few AR focused companies that have gone under.
I have seen a few builder kits (with decent parts) for as low as $269, so add a blem $50 lower and $319 is a pretty good deal. I still have not seen one I would actually consider owning for less than $600 though.
If you buy an AR15 today for $400 as an investment, you are gambling that you will be able to sell it for about $700 in 4 years or $1400 in 8 years. While I know a guy with a pallet of ARs he bought at $520/unit (100K of ammo too) for an investment, I am not convinced it is a good risk to reward play.
But yes, the AR market will survive, and in some segments thrive. All the small companies are scrambling to get AR9 parts in play, and some are junk, but some are pretty good. More and more people are hunting with ARs as well, so those more potent calibers will see some improvement in the next few years.