If a player messes up a crucial die roll that will change the entire outcome of the adventure for the worse, you can always give them a chance to recover the situation. Just come up with some plausible reason why they might be able to modify what they've done in time for it to make a difference.

It doesn't even have to be all that plausible. The players will go for it.

Actually, 90% of the time they'll be all too happy to come up with the excuses for you. All you need to do is listen to them try to justify why their cockamamie ideas might conceivably work if you tilt your head sideways and squint at them for long enough. Then pick whichever sounds the least ridiculously unlikely and ask for another die roll.

(You don't have to do this, of course, if you'd rather the real drama and tension of the adventure literally hanging on the outcome of one die roll. Which is also a valid approach in some circumstances.)

Transcript

Luke: So... uh... Ugh, 9, is that enough?
R2-D2: Aww.
GM: The torpedoes blaze towards the vent, but look like they're going to pass straight over the top...
[SFX]: Whooosh! Whooosh!
Luke: Oh come on... turn... turn damn you! Into the vent!
GM: You're trying to steer the torpedoes? Like... trying to will a bowling ball away from the gutter as it rolls down the lane?
Luke: Uh, I guess so.
[SFX]: Whooosh!
GM: Make a roll.
GM: With a normal die, please.
Luke: Um... 16?
GM: The torpedoes veer downwards...
[SFX]: Whooosh!
Luke: Come on!
GM: ... heading into the vent...
All: Come on!
GM: ... and straight through the tiny hole in the grille!
[SFX]: Whooosh!
[SFX]: Whooosh!
{beat}
C-3PO: And then?