As of right now, the bitcoin price is expected to keep going up in the next 20 years. But can it last that long? I believe it's possible. But can't it crash at a random time? Like the price going down hard.
As far as i know, there are only limited sources of bitcoin for about 21,000 i think. And we already mined for about 16-18k. Maybe if we already reached the limited amount of bitcoin, it will be gone. Or maybe some will trade, buy and sell and i think in that time, bitcoin price will be very high.
Your numbers are way off, the limit of bitcoin is 21 million and not 21k and the amount mined already is something close to 16.5 millions coins and every 4 years there is something called the halving, this cuts in half the block reward that miners get for solving a block, that means that as time goes by less and less bitcoin is created every year this makes bitcoin a coin that has a very low inflation rate compared to other currencies of the world.