The First Order may be a can of Diet Empire, but they are still active by the end of The Last Jedi.
In Return of the Jedi, the Empire wasn’t really technically defeated, only the guy running the show was taken out.
It seems pretty obvious, but The Resistance still has to defeat the main bad guys of the series.
We can’t say for sure if the whole First Order will be dismantled by the end of Episode IX or if they’ll only be left leaderless, but The Resistance will have to come out on top all the same.