Exactly. If prices go up according to supply and demand, then Bitcoin could be a sustainable cryptocurrency for the foreseeable future. The genius deflationary design by Satoshi Nakamoto, will allow Bitcoin to remain a valuable cryptocurrency in contrast to Fiat. Of course, volatility is still a huge issue related to Bitcoin and other cryptocurrencies. But, the emission rate of Bitcoin will keep it going for many generations to come.
While we're still far away from the year 2100, Bitcoin's circulating supply has come a long way since 2009. If fees on the network remain as low as possible, then people will continue to use the Bitcoin blockchain as an alternative to traditional Fiat money. In effect, this will allow miners to retain a solid income stream even after all 21 million coins had been mined.
Nevertheless, as we go close to the hard cap of 21 million coins, Bitcoin's price becomes higher. And then, we would be dealing with "satoshis" of a Bitcoin, instead of a half or full Bitcoin. Just my thoughts