Comment: Same Way You Should Do Everything Else For Them (Score 3, Insightful) 292
You do it well. You've obviously already determined that they're planning on cutting costs by getting an in-house developer to take over, and I'm assuming you know that means they're not planning on keeping you on that particular project forever. So rather than doing a half-assed job and leaving the newly-minted dev with the codebase, a handshake, and "good luck!" do them a favor and help them learn everything they should know to do a great job. You really have nothing to lose by training the new guy well; you've got other clients lined up, if you do a good job this client may have you come back in the future (when the economy has more fully recovered) and do more work for them, and you'll have built another relationship with a developer who remember that you took the time to help them out.