Aw, come on now. They saved them fair and square within the bounds presented to them, and they almost certainly did it because they genuinely liked them. And you cheated them out of that win for... what?

Don't let your attachment to a pre-conceived idea of how things will go cause you to deny your players something that they've rightfully earned, especially when it's likely a small flavour thing that they care about. That minor NPC isn't going to break any plots or questlines.