They'll definitely get Sigourney back, you can count on it, but they'll also probably want pass the torch to a younger actor. It'll be the same shit that Star Wars is doing now.
I don't find that a bad thing. I think passing the torch to Newt and/or additional characters would feel satisfying, especially after giving Ripley's arc an ending that it actually deserves that isn't just a poorly-executed "back to zero" move. Look, I don't have any inherent problem with doing that, if it's done well. Take Rocky 6, and having Adrian dead from cancer and Rocky as a restaurant owner. It's unexpected and certainly something many fans wouldn't initially like, but it's handled in a manner that not only feels like a logical progression, but provides a great subconscious reason for Rocky to go the distance one last time. Just killing off Hicks and Newt off screen is so f**king disgraceful, and just throws the fans and those characters under the bus, making it feel that the great sacrifice and effort to save them utterly pointless.
And honestly, I don't really get how the Star Wars fans can just fracture so much, worse than ever before during the prequels. Look, I love the original trilogy, I love the prequels, and I love what has happened on the big screen since Disney bought Lucasfilm. It's of the scope and scale that this massive saga deserves, and it enriches not only the characters, but their stories and the various environments in ways that still manage to surprise. Simple fact is that many of you want Star Wars to take risks, but only the risks that YOU approve of and have settled upon years ago. And because it upends what you thought the world of the saga was, because it completely shatters your notions of how you saw it, rather than simply admit that you were wrong, you say that "things WERE this way, but they changed it to spite us! f**k THEM ALL!", and never bother to understand how this could be the logical end result. Simply put, the problem isn't the films, the characters, the effects, or anything like that. The problem is you and your inflexible, arbitrary standards. The same line of thinking completely runs through the reaction to Disney's filmography, animated or otherwise, as of late, of an increasing backlash for the direction of the Evil Dead franchise, of slamming popular anime series, of dismissing any Call of Duty installment, of the hipster hate and gaslighting over the merits of Final Fantasy X and X-2 and Advent Children, of the "Metallica are sellouts" argument, of the undeserved overly negative reaction to Prometheus and initial mood of "vastly improved" for Covenant, or calling Steven Spielberg well past his prime.