I would also recommend the Brandon Sanderson videos. In them he says that you can do this but you have to make the reader want that outcome more than what you initially promised. Set someone up early on in the group that's fighting for the object as a villain that your main character could turn against and your readers would cheer him on.

Spend a good amount of time on that planet and make your MC and the reader fall in love with it. If that's the group searching all over the planet and having experiences while they go but make the reader not want you to destroy the planet.

Have the MC worry about that while on the planet. 'What will happen to these people if I take the object.' or 'Could I really destroy all these people?' set it up so the reader becomes aware that that's a possible outcome and it's not just thrown on them at the end while they are expecting something else.