Well, closure for anyone that was worried.
I went out first thing this morning to get the paper, and noticed all of our mailboxes were opened and mail scattered in the road. The trick package was missing!
I picked up about 30 pieces of (mostly junk) mail and put back in proper mailboxes.
I am probably done with this line of revenge, I was worried, too, that it might end up back in the postal system and cause a huge stir and possibly legal problems.
I'm thinking a better 'trick package' may just contain an official-looking note and some kind of RFID tag making it seem like it's traceable.