We don't really need BTC. I hate when I see people trying to convince others to sell everything they have to buy BTC, it's disgusting. Bitcoin is a lottery, you shouldn't use the money you need to pay your bills and buy food to bet in the lottery right? Bitcoin is kinda the same thing. People should invest money that in case they lost it wouldn't be a big deal you know? It's a long-term investment, however, it's a bet. You can win a lot or you can lose a lot too. Are you brave enough to deal with this risk?

The only honest answer is: for as long as two people or more believe Bitcoin has use and value.

The schedule for block rewards is set to extend out to the year 2130 so bitcoin mining (in its true sense) can continue for that long as long as there are transactions to produce work for.

Maybe an equally good question is: what could end bitcoin? If we think about it from that perspective we can identify what threats exist to seriously harm bitcoin.

One such risk is Governments. They can ban the use of bitcoin among retailers which would seriously diminish the opportunity for adoption growth.

What else?

I would recommend to start with reading the Bitcoin Whitepaper, most people who get into crypto skip this step and I it's a fundamental step to understanding what cryptocurrency is designed to be. You can find it here, this is how it all began: https://bitcoin.org/bitcoin.pdf