From an EU fan's point of view, the alien is the reappearing star, just as nanison said.
But from the studio's point of view, following Aliens, a Weaver-less Alien film would be like a Die Hard movie without Bruce Willis.
With Prometheus, Ridley Scott had the power to convince Fox that he had the ability to kickstart the franchise with a completely different vehicle to drive it forward—namely, the dangerous android narrative, with Fassbender as its star.
As for a reboot: There's a reflex reaction against such a thing by many fans, because traditionally a reboot means the studio retires all support for the old stuff and encourages the fans to forget about its existence too, putting all their support behind the new reboot instead. When films were exclusively distributed in theatres, it made good business sense not to have your new stuff competing in the same marketplace as the old.
But that's rather old fashioned thinking. These days we have home video and streaming with which audiences continue to revisit original films at will. And philosophically, the current storytelling landscape is showing us over and over again that "alternate universe" stories are valid forms of franchise-making, especially when jumping to a different medium.
Quite apart from Noah Hawley's project, I could see a "remix" of the entire feature film series (and even incorporating EU material like Seegson, the Cold Forge, etc) rewritten as a streaming show, pulling Shaw and David, Ripley, the Nostromo, Hadley's Hope and Newt, Fiorina, and the Auriga all into a single, contiguous, saga, not being spread out over a hundred year long narrative the way they currently are. The kernel of the plots would remain, but the characters and details of the storylines would be reimagined, much like Marvel's "Civil War" comic book was reimagined for the Avengers MCU.
TC