The thing about running a game with a grand plot that plays into the hands of epic literary tropes is that you don't control what the players or the dice do. If you're writing a novel or directing a film, you can make the story follow the mythic arcs, because nobody will be doing bizarre things of their own free will within your story and no random events will suddenly change things without you being able to do anything about them (without being accused of cheating).

So although you may set up something to generate a brilliant piece of storytelling, always be prepared to have it dashed in a single moment of unavoidable action by a player.

This is not a tragedy though. For when you do get one of these setups to work, it will be all the more memorable for both you and your players. The interactive, group-created fiction of a game can be a pale imitation of the best single-author fiction. Or it can tower over it. You just have to give it the opportunities.

Lots of them.

Transcript

GM: Jango Fett appears next to you, shooting at Jedi.
Mace Windu: I run up and hit him!
GM: He fires at you... but the shot goes wide. Make an attack roll.
[SFX]: Whooom!
[SFX]: Krtshhh!
Mace Windu: 20! I cut his head off!!
GM: Er... okay. His helmet falls to the ground and he falls over, dead.
GM: Boba watches in horror.
[SFX]: Thunk!
Mace Windu: What? Dead? I only wanted to stop him hurting everyone. I take it back!
GM: Um...
Obi-Wan: No, Sally, it's okay. He would have killed lots of people. He was my arch-nemesis.
Mace Windu: Your arch-... anemenis?
Obi-Wan: He was a baddie, remember.
GM: Yes, he was very bad. You did a good thing.
Obi-Wan: I mean, it would have been fitting if I got to kill him, but...
Mace Windu: I really need to play someone nicer.