How do you gradually shift responsibility for a system to the customer?  How do you reduce the risk of a customer inheriting a system they can’t sustain?  Rather than outsourcing, you can consider “insourcing.”   In Extreme Programming Explained: Embrace Change (2nd Edition) (The XP Series), Kent Beck writes that insourcing is where you gradually replace the members of the team with technical folks from the customer.
Gradually Replace Team Members with the Customer
Beck writes:
The “big thump” delivery of outsourcing violates the incremental change principle.  There is a slight twist on outsourcing …

Adding people to late projects makes them later.  This can be counter-intuitive.  In Requirements-Led Project Management: Discovering David’s Slingshot, by Suzanne Robertson and James Robertson explain how adding people to late projects makes them later.
The Least Knowledgeable People Prevent the Most Knowledgeable People from WorkingAccording to Suzanne and James, adding people to a late project, makes the project later:
The problem of adding people means disrupting the rhythm that your existing team has established.  It increases the number of communication paths. New people penalize the existing team.  When new members arrive, …