I heard about such a strategy - to buy alt-cues cheaper than one dollar from the first 20 at coinmarketcap. Perhaps it is worth trying this strategy. I do not think that such coins will leave the market when they fall.
The truth is that such project who has made to the top 20 on coin market capitalization would have sufficient capitalization to remain relevant for a long while. Though it is possible that the team abandons the project, but in most cases they are viable. Another approach is by diversifying your portfolio to include projects that are of great potential and still upcoming. A good buy is MPCX who has a partnership with IBM and would be holding its IEO on OOBTC exchange and PROBIT exchange on the 28TH OF JUNE, 2019. The token would be sold for only 6 cents.