Though very unlikely in my opinion, $43 is definitely not impossible. But imagine the number of buyers there will be from bitcoin dropping to below $1000 alone. I'm pretty sure there's going to be A LOT, including me. Bitcoin at $43 isn't bitcoin being dead though, it's just bitcoin in a significantly lower price. The blockchain will still be up and running, so I'm pretty sure there's no death that's going to take place there; even if bitcoin drops to $0.01.
Here's a fictional scenario:
At lower prices, most miners will pack up, opening the threat of a 51 percent attack by criminals. If they target the first million coins (in Satoshi's wallet), it's essentially GAME OVER for the integrity of the Blockchain stands permanently compromised.
But, seriously speaking, is that plausible in real life? DYOR!