the congestion really has only just begun. if it persists, yes, ppl will start to stop using Bitcoin. the exit starts slowly at first and then will morph into a stampede; especially if the price starts plunging. the mempool is a problem that does have to be fixed so that ordinary users can start getting their tx's through. they won't be as patient as some of us here.
In 5-10 years I can imagine having a handful of dominant blockchains that run in parallel. Today we have Visa, MC, Discover, and AmEx; tomorrow we have bitcoin, litecoin, monero, whatever. Actually we will STILL have Visa, MC etc but they will each utilize multiple blockchains as behind-the-scenes payment rails. If one blockchain goes down, Visa (or whoever puts Visa out of business) will switch to another until the problem is resolved. (All behind the scenes as far as John Q Public is concerned.) If not resolved in a timely manner, miners shut down due to reduced transaction fees (after days-weeks, maybe months of downtime), and that chain suffers. If all major blockchains are running smoothly, then the preferred chains would be the ones with the widest acceptance - just like credit cards today.
It would take a lot of downtime though to kill off a prominent blockchain. It takes time to build up lots of hashpower. And even if miners turn off, where are they going to go, and what prevents them turning back on, once the technical problem (whatever it is) is (hopefully) fixed? Presumably, the major competing blockchains will not use mining equipment that can be switched from one blockchain to another.