I'm not imagining players who lack motivation, but ones that are okay with bad things happening. They will certainly attempt to save the princess from Bowser both because that's the plot and they have built up an attachment to the Princess NPC. But if they fail to save her, they roll with the punches because whatever happens next is also consumable plot - either resurrecting her, rebuilding the kingdom after her loss, etc. Heck, they might even think the princess dying is more interesting. They're not playing villains, but the players themselves are eager to see what happens next now that things have taken a turn for the worst.