An in-game wedding is a great chance for characters to let their hair down and celebrate something. Which can make a nice change from grinding through dungeons or battling the forces of evil. Or even outrunning the authorities with your stolen ship.

You could set up the wedding and have it be crashed by said forces of evil (à la Bill Weasley and Fleur Delacour). Or you could simply make the players paranoid that the wedding will be crashed in some disastrous manner... and then have it not be.

Transcript

Luke: Hang on, you mean for real?
C-3PO: You got engaged?!
R2-D2: What? To be married?
GM: Congratulations!
Chewbacca: That's awesome! I'm so happy for you!
Luke: You mean they weren't already married?
C-3PO: No, you dork!
Han: Thanks, everyone.
C-3PO: Have you set a date?
Leia: Not yet. But you'll all be invited.
GM: An Ewoc sounds a celebratory trumpet.
[SFX]: Barroooogaaahh!!
Wicket: You've saved our village! Thank you!
Chewbacca: From the Empire? Or Nute Gunray?
Wicket: No, we were doing quite well from those. But the new business from a Princess's wedding should more than make up for it!
Leia: I really need to change my name.
Han: To Princess Greedo-Organa!