Yes, there is a Star Wars story in which Greedo kills Solo and the Death Star isn't destroyed just then. It gets destroyed at another moment in time and by other means. If you're forcing the story to follow the footsteps of A New Hope then not only are you missing out on a great set of alternative outcomes, you're setting yourself up for a load of game mechanic pains.
The first step I take to achieve this is realizing there is always a bigger story and the initial plot line need not be the actual outcome. This requires that a) I have less of a reliance on the expected events occurring and b) have a backup plan. Realize that the world the characters are living in is a live and dynamic environment. It will continue to evolve as the characters interact with it. It isn't waiting for a preset of events to occur. It doesn't have a preset set of scenes and images like a computer RPG has. Don't throw away the greatest advantage a tabletop RPG has over a computer RPG!
Here are some guidelines:
- Don't rely on a character or set of characters to make it to the end.
- You should not fudge the rolls or bend the rules to force an outcome that's needed to follow the storyline.
- Don't fudge to open a door
- Don't fudge to save a party member
- Don't fudge to convince the gatekeeper
- Don't rely on a single character in the end scene. Actually now that I think about it, don't have a preset ending scene.
- If something needs to happen and this depends on a die roll or the application of some rule with random outcomes, then there is something wrong with the adventure. You must either make the event independent of die rolls or have an alternative to handle a failure with the dice.