I think we've got a fair amount of life in the line yet, but if we do reach the point where it ends I'm sure I'd be buying something else. I sort of get the feeling that if Hasbro lets the line/contract lapse, that some other company would love to pick it up just to do their own take (whether it be 6" scale or something else), so it seems like there would always be some sort of SW line even if it was a more focused "collector" line (exclusive to online, TRU, etc.) Otherwise, I buy Marvel stuff too, so I'm sure there would be something to buy.
That being said, it would be a nice place to cut things off a bit too. I've been putting off completing the vintage line (loose) for years now, and it is one of my "eventually" goals. I'd probably move on to that, and pick figures up here and there while working towards that goal. If I reached that, I would maybe look at other vintage stuff....or just save the money.