During the gameplay presentation of The Last of US 2 during the E3 2018 Sony event, we attended a long sequence with Ellie. A sequence that could leave the doubt as to whether Joel will be playable or not. Indeed, during the discussion scene between Ellie and her partner, Joel is mentioned during the speech.
This already proves that the character is alive and well and that he will have his role to play during this second adventure. Nevertheless, The Last of US Part 2 will focus more on Ellie ! In an interview, Neil Druckmann, the game director said that Joel will not be playable in this sequel.
Be careful though, Neil Druckmann might very well want to keep this information secret until the game was released although the gameplay sequence shown at E3 to the public, but also the extended version of the demo presented behind closed doors confirmed that Ellie was the main protagonist of the game in all cases.