People who think that Bitcoin is going to zero are likely mistaken. The design is robust enough that it will continue to exist in perpetuity, barring some currently unforeseen breakdown in cryptography or a surprise 51% attack (even then, a fork would carry on I would imagine). What is can do, though, is decline to a price consistent with hobbyist tinkering. Because it is a complete failure as a currency, as a store of value, etc., it isn't going to become the dominant money of the future. So I'd suggest a 2050 price target of under $10,000 in today's dollars. Possibly much lower.

Sorry sent that too quick. There are similarities and differences. Gold has other non-monetary uses. Gold will continue to exist at zero cost because it's an inert physical thing, whereas the current ongoing cost of keeping btc rolling is still quite a lot. (That'll drop too, of course, if and when mining gets cheaper, which is part of why I don't think it will go to zero.)

Let me give an example. I live in the UK. I want to send my friend £10. He gives me his bank details. I send the money. Bank fees? Zero. If I want to do it via BTC? I have to buy BTC (bid/ask spread), send BTC (transaction fees), my friend then has to convert back to £ (bid/ask spread). It's... stupid. No one is doing it because it's stupid. No one will ever do it. Except hobbyists.

@stephenz010 Also my point is that it won't go to zero. A hobbyist community can and will carry it forward indetfinitely.