High network fees will force people to leave their coins on centralized exchanges and/or centralized wallet providers (also known as custodians). But I wouldn't worry about this, since fees are not meant to stay high forever. At some point, they will decline back to considerable levels. As of now, network fees are cheap again. I'm certain developers are continuously working on scaling the Blockchain to help prevent fees from spiraling out of control. A quick solution would be to introduce "fractional satoshis" for cheaper transfers.

No matter what big exchanges or institutions try to do, they won't be able to buy all of BTC's circulating supply because some people will resort to self-custody. That small percentage makes a difference. Hopefully, Bitcoin stays decentralized and censorship-resistant for generations.