Do you think that after voldemort died, there would be a wizard equally as bad, or worse that would come?

maybe, but probably not in Harry's time. But Voldemort was pretty powerful and gifted. I mean, being the heir of Slytherin is not something anyone can just be. And there was Dumbledore. So I think in just a lifetime there's only a few great wizards that are extremely powerful and wise. It all depends if they're good or evil.