The most obvious thing to do is have the NPC be replaced with a doppleganger minion of your next big bad so that the sending stones end up passing along disinfo (splitting the party, giving wrong directions, getting them to discard a magic item under the false belief it is cursed, etc)
Why is work so important for you? I think you’ll find that a large number of people simply go through the motions because the stakes are low and their lives outside of work are more interesting. To them, it is an exchange of labor (that isn’t valued anyway) for (not enough) money. Why push yourself at work when it simply doesn’t matter? And what will drive you nuts later is that people from that “lazy” group will eventually end up promoted over you. The work is ultimately inconsequential, but the relationships built matter.
I don’t really have an answer for you other than to introspect a little bit on your work ethic.
You’re not wrong, however, they can have their toys back after they figure out what happened and rescue the NPC. It’s a good hook and requires them to think about spending some of their treasure to shore up their home defenses. For all we know, their players are murder hobos and this is well deserved comeuppance.