No one knows what exactly will happen in the top 20 of the crypto market in 2 to 3 years from now, but, I am sure that those with a strong foundation, dedicated dev, innovative marketing plan, and solid community will remain. There is possibly a new project to emerge on the top 20 and possibly some will cease to exist, after all the crypto market is like a jungle where the survival of the fittest exists.
dev team and project that could deliever and improve their MVP regularly will stay in cryptomarket , even they could cease other project quit from top 100 or even top 20. some existing project in top cmc have no this, they fell comfort with trading volume in market and didnt give any new update. soon or later new project will shift them.