Insects probably – it’s been suggested that if there was a nuclear war that wiped out humans then cockroaches would take over the earth as they can survive almost anything! Eughh – not sure I like the sound of that!
I think that may be impossible to predict. Another “intelligent” species could evolve, but similarly the world could be left with nothing but microbes, as it was for a couple of billion years before animal life evolved. It would depend on what the environment became like, because that’s what drives evolutionary changes.