Re: "I shoot the escape pod!!!"
On the question of players totally zapping a planned plotline, I can't directly answer, as it hasn't happened to me on that level yet. I think that if it does, my response would be, "Well, that's why we roll dice!" and go on with it. On smaller derails, I generally congratulate the player (if the derail is done by cleverness, rather than lucky dice-rolling) - AFTER the session is over. Scrambling to determine what the villains would do in such an unplanned situation is something I enjoy.
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On the Star Wars thing, the whole plot is on rails throughout the entire six movies - "It's the only way" et multiple cetera. One example - if on Tatooine needing to fix the hyperdrive, Qui Gon Jinn simply Jedi Mind-Tricked some random person into thinking that Republic credits were good and had that person buy the hyperdrive from Wattoo, there wouldn't have been a need for the "Hold your fire" line!
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I rather enjoy the players coming up with things I didn't plan for. One example - a mercenary group attacked the PCs; they fought off the attack, and the mercenary sargeant took off running. The stealthy PC took off after him, and managed to pickpocket his sword and dagger, then yelled, "Surrender!"
The sargeant turned and reached for his sword - not there. Then reached for his dagger - not there. The PC then displayed both weapons.
His morale broken, the sargeant said, "Okay."
The party ended up hiring him and the survivors of the unit - and paid the two severely injured members of handsomely. The unit served the PCs with high morale. Totally unexpected, and great roleplaying!