https://gamefaqs.gamespot.com/a/forum/c/c4fbc6f8.jpg
Obviously, it wouldn't have Schwarzenegger and Stallone battling Disney-owned xenomorphs and facehuggers. Even if the two seventy-somethings were down for it, Disney's lawyers would come down so hard on Konami that death by chest-bursting alien would feel like a merciful alternative.
So, who would they fight? I could see the giant turtle from Contra 3 making an appearance. The alien boss in the American football uniform from the first game too. They'd probably have human soldiers (or mind-controlled zombified human soldiers) as the main enemies for budgetary purposes. They would definitely have one of the women from the later sequels join in the action.
Even if the designs of the first game weren't a little too close for comfort, film adaptations of video games rarely adapt the first game anymore. They usually go for an original plot which attempts to capture elements of the franchise as a whole.