If Newt had lived, she could have easily been recast after a time jump for a hypothetical Alien 4. It happens all the time with child characters who grow up. I generally hate recastings and even that sort of recasting doesn't bother me.
And I'm not sure her survival in the scenario I proposed would have been any more of a distraction to the audience than either her death or the baffling presence of an egg on the Sulaco.