I don't know if you are aware about the fact that by the time the last satoshi is mined, unfortunately according to the laws of physics... we will all be dead:
If I remember correctly, the last satoshis will be mined in around year 2140, so good luck with that.
The good news is, as you can see, the asymptote becomes almost flat in around 2029. Which means, anyone holding 21 bitcoins, or even a single bitcoin, should be very wealthy by then, assuming everyone goes the right way (no big block agenda ruining the decentralization of the network by nodes being too big to run killing bitcoin as a decentralize store of wealth etc).
If we can keep those basic pillars intact, BTC will simply continue to grow.