There used to be demand for gold, it used to be the universal currency and some national currencies are still linked with gold (so most people don't even need to own actual gold). The US disconnected the dollar form gold since Nixion was president and that is the only reason it seems like there is no demand for it, but let's be honest here bitcoin doesn't come anywhere close at the moment, even though bitcoin works much better as a currency.
If scarcity is the main factor that gives value why are 90% of alt/shitcoins completely worthless? Just because there is a supply cap doesn't mean people will jump hoops to get it.
In the world of cryptocurrency, the one with the first mover advantage is the be all end all. All other altcoins that comes after the first one will basically have to be based on the first one, even though and no matter it has better features or not. The way cryptocurrencies work or even exist in the first place is because of Bitcoin. So Bitcoin can't ever die, just like Internet can't ever die. It's a protocol. There may be an Internet 2.0 if there needs be and in the same way there will be a Bitcoin 2.0 if there needs be but it won't ever disappear.