If the scalability of bitcoin grows very slowly, bitcoin will gradually continue to lose demand and the level of capitalization, until the price ceases to dominate the price over other types of crypto currency. As soon as this happens, bitcoin will lose everything and at best remain an honorary crypto currency with the use for expensive transactions. The truth in this case is very difficult to predict its price.
That's certainly true, mate. Many people are in it for short term profits, instead of using the cryptocurrency for daily transactions. Whenever the network load increases, fees rise, and newcomers into crypto become completely disappointed (which results in massive sells within the market). The situation becomes worse if Bitcoin doesn't scale to handle large amounts of TPS for people worldwide. It'll still be the "digital gold" of cryptocurrency, but it won't fit its purpose as a Peer-to-Peer Electronic Cash System.
If scalable solutions such as the Lightning Network and Sidechains become successful, then without a doubt, Bitcoin will scale to millions of users worldwide. I believe that the process for this to become a reality has been quite slow simply because developers want to make sure Bitcoin scales safely without sacrificing its decentralization. Of course, it's difficult to predict its price (as Bitcoin is volatile), but it'll be here to stay for many years to come.
Therefore, no matter if Bitcoin scales or not, I believe that it will continue to exist as a decentralized cryptocurrency for many generations. No one or nothing can stop Bitcoin, as it has grown too big to fail. However, only time will tell us what lies ahead for the longevity of Bitcoin as a cryptocurrency for the masses. Just my opinion