Lore wise, Cayde never really "died" in his previous life, his consciousness was just transferred to an exo body, sort of like Jake Sully in the James Cameron's Avatar movie. But even if let's say Cayde did die in the next expansion, he's a guardian, his ghost would resurrect him. As Ikora said in the D2 campaign, regarding Zavala, "He doesn't realize he's died his last death." She is referring to the ghosts' inability to resurrect guardians due to the cage over the traveller. That is no longer the case however, as all guardians have reconnected with the traveller, and in turn reconnected with the light, and do not die permanent deaths. As that is the very essence of what makes a guardian a guardian. They are warriors of the light for life, and for all of their lives. Not speaking lore wise and just speaking from a game perspective and even a marketing perspective to a point, Bungie would never kill off Cayde. He's the most liked character in the Destiny franchise, and finding a replacement fan favorite this deep into the franchise's life would be very difficult for them.