It's true that we see Talos' true Skrull face when Gravik stabs him, but we don't get a clear look at him after the villain lets him fall to the ground. This effectively negates the surefire Skrull tell of reverting to their true form shortly after death, so let's embrace the possibility that "Talos" may have been actually a completely different Skrull. As for Talos himself ... well, when you're impersonating people, why not go to the very top and assume President Ritson's (Dermot Mulroney) identity? Hey, Nick Fury did tell James Rhodes (Don Cheadle) that there's a Skrull at the very top level of the country. Who's to say he was speaking about Rhodey?
Given the stakes of "Secret Invasion," it's only natural that Ritson appears in the show. However, he seems a bit bad at his job, doesn't he? As noted in Episode 4, the President can barely make an informed decision without outside input, and indeed, he seems to be a little bit snarkier and more out of his depth than you'd expect from a powerful man ... much like Talos when he impersonated Fury in "Spider-Man: Far from Home." So, maybe Fury and Talos went directly to Ritson after learning that Rhodey is a Skrull, and managed to convince the President to stay safe while Talos takes his place.
As for who could be playing the Talos role, we've seen very little of the Skrulls who might still be loyal to Talos and Fury in the show — such as the unnamed Skrull agent (Lori Livingston) in "WandaVision." Narratively, the most impactful Talos impersonator would probably be Soren (Sharon Blynn), Talos' wife. Gravik's people are supposedly responsible for her death, but it could just be a story Talos tells to maintain a deep-cover situation. If she is indeed impersonating Talos in Episode 4, the cover story would become tragically true and Gravik would end up killing Soren for real.
