Your manager is unlikely to know just how unmaintainable of a mess you have created until you are gone, and by then it's too late to be helpful to you. Certainly he wouldn't re-hire you to continue twenty more years of unmaintainable code. No... by the time he finds out what a mess he has, you would already be gone, and when he finds out, you will never be invited back.

Furthermore, the new, highly motivated, cheaper salary individuals will have such a hard time figuring it all out that they too will be unproductive. But this is a global marketplace; if it becomes apparent that, whatever the reason, your geographic region is unable to provide trustworthy, well-written, maintainable code, your entire region suffers. The client comes to the realization that it turned out to be no bargain, hiring the overseas company at 1/3rd the rate of programmers they can deal with and supervise more intimately in-house or in-region. While they were paying "oursourcing" prices for the product, they are now suffering a "local-region" impact to their business, in their local-region currency. They have lost control of the code base on which their business depends.

It is this sort of issue, I suspect, that keeps in-house, or in-region programmers highly employable.