Ethics

Someone I know hired a landscaper to build a stone patio in his backyard.  The landscaper completed the job, and the person I know never heard a peep.  No bill.  Nothing.  After four months or so, it became increasingly apparent that the landscaper had dropped the ball (or perhaps the hedge clippers) and had somehow neglected to bill the homeowner for the patio, which probably would have cost in the neighborhood of $3,000. 

So here's the puzzle for you ethicists out there.  Does the homeowner have a duty to notify the landscaper about the bill?  If so, how long should the homeowner wait?  If you think the homeowner has no such obligation to notify, what's your reasoning? 

Although it's not a legal ethics problem, I found the issue to be ethically and morally interesting, especially since the homeowner in question has gotten a wide variety of answers to the question.  How would you legal ethicists out there have advised the homeowner to proceed, and why? 

Update: In addition to reading the insightful comments posted below, you can read my additional thoughts here.