'ALIEN' didn't need a sequel.
If Cameron hadn't been brought on board as a director, his 'Mother' script would have been made into a different property launching movie, the first of many.
As for killing of the series. No. 'ALIEN 3' did not kill it off. 'ALIEN Resurrection' followed, so there's that. The series kind of diverted with the 2 'AvP' movies and it is now healthy again. 'PROMETHEUS' and 'ALIEN Covenant' are much better movies than some people would have you believe.
Oh, sure. The precious fanboi Blomkamp retcon got canned. Too bad; but that was a good move to lose that. Nonetheless the whole "I don't like the new movies." attitude is a failure to manage expectations more than anything else - and is not the fault of the movies themselves.
The series is healthy now as it ever was. There's a ton of licenced content in every form. It's only been 2 years since 'Covenant' was released. We'll get another movie sometime.
So no. 'ALIEN 3' did not kill the franchise. lol.
What needs to die is the whole precocious attitude that only the first 2 movies matter. That's a poor state of play we must get around and put aside. It's just a form of fan bigotry. You don't see fans of movies post 1986 'ALIEN/S' movies pointing the finger at the first two movies and getting away with "they suck!"
This attitude has to change.