The blight is an extension of the actual invaders' homes. i.e. the "blight" was assuming the metaphysical properties of a completely different plane of existence. Even if the blight ever lifts, the invaders' home planes would remain inimical to human life. Entering such a place unprotected would still result in your immediate death. As I said, if you wanted to "invade the invaders" you would have to find some way to stay alive in such a hostile environment.
I don't think there is, but who knows.
Many stuff has been proven not to work.
