Here's how Bitcoin becomes extinct, or, like the Coelacanth, becomes very rare.
1) Price continues to drop. BearWhale comes back and dumps a load, causing fellow whales to dump a load, causing feedback that causes a crash back to the teens
2) Media picks up on 1), says: "
BTC dead"
3) Congressmen, like Charles Ellis "Chuck" Schumer, who is a
BTC-hater, start zeroing in on more Bitcoin regulation, like Schumer's proposed FinCen stuff. This might increase if the Republican's lose the Senate in November, or, if bitcoin is linked to the 'war on drugs' it might not matter if the Republicans win or not.
3b) ...FinCen will require each and every Bitcoin user that uses a US-based bitcoin exchange to file paperwork every year if the amount transacted in one year surpasses 10k USD.
4) Due to technical factors like the increasing size of the blockchain, a lot of users will start using online wallets. This will negate privacy due to 3b)
5) other crypto-coins that have more inflation and more transparency will be seen by corporations as more stable.
5B) Walmart and others adopt "CircleC":
https://www.cryptocoinsnews.com/apple-pay-rejected-by-walmart-and-best-buy/ and they specifically reject Bitcoin
6) another major Silk Road bust occurs. Already Silk-road substitutes are in greater demand and in greater numbers that before (source:
http://www.coindesk.com/silk-road-one-year/ ). This scares Joe and Sally Average into dumping their bitcoin, especially when Schumer attacks bitcoin holders as promoting drug use. Drug lords switch to DarkCoin or some other cryptocurrency and this snowballs amongst actual users of Bitcoin (as opposed to the buy and hold speculators).
7) A hard fork or some technical glitch (like
https://bitcoin.org/en/alert/2013-03-11-chain-fork) knocks out bitcoin, further causing big corporations to distrust it
Anything else? I'm sure I forgot something...list your FUD and bugaboos here!