"surely there is a future hope, and your hope will not be cut off" (23:18). What does the saying say about that hope, and what doesn't it say?

The saying follows a command, and gives its reason: "Don’t let your heart envy sinners, but rather fear the LORD all day long. Indeed surely there is a future hope, and your hope will not be cut off" (23:17-18) (tap envy, hope). It doesn't say what the future hope is, or when it comes, and these notes don't either. The same Hebrew words come again at the end of a saying about wisdom: "If you have found it, then there will be a reward: Your hope will not be cut off" (Proverbs 24:14). There the WEB gives the word of 23:18's future hope as reward (tap end), and a few verses later it says, "for there will be no reward to the evil man" (Proverbs 24:20). These notes quote the saying as it stands; they don't make it a guarantee of any outcome in this life, and they don't explain it away.