Bitcoin at that price would die due to low security and constant attacks - every script kiddie could target it with a medium-sized botnet.
99.999% of miners would abandon it completely, aside from a few hobbyists, because no one mines without profit.
So why would anyone buy it? I'm sure there would still be people willing to buy, but it would be like purchasing a dead scam coin that pulled a rug pull ten years ago.
You think? What if Bitcoin is merged-mined with other cryptocurrencies? Just like how Litecoin is merged-mined with Dogecoin these days. That will ensure BTC remains resilient against external attacks.
Developers also have the choice of making Bitcoin a hybrid PoW + PoS cryptocurrency to protect the Blockchain against sudden drops in network hashrate. Peercoin and Decred are good examples of this. Considering that the USD is losing value, don't expect BTC to go back towards $500 anytime soon. It's already too late for that.