It will be interesting to see where the line will be headed once the CW is over - that is if we don't see other media support. I mean really, we haven't known Star Wars without some sort of current media (OT special editions, prequels, animation) for a long time now. Sure, there were the "between" years, but this would be the first time in a long time without anything to look forward to.
I would also be surprised if something else wasn't lined up by then too. Lucasfilm really seems solid with the "Star Wars is forever" thing, and there has already been rumors/confirmations of further animated series beyond Clone Wars (the Seth Green project, etc.). Plus, the whole live action thing if/when that happens.
I think Adam at GH touched on something similar to this in his Q and A this week (regarding the SW line's longevity and collecting), and I've seen discussions lately about action figure lines in general as Mattel tries to drum up support for its DCU subscription service. Action figure lines in general just aren't what they used to be - and most (movie lines) are the passing fad each summer/year with kids. It is the collectors that keep the continued life these days I think, regardless of what they might hope or say. I just don't see many kids stick with a property that long, particularly if there isn't media support.
I'd have a difficult time seeing Star Wars die off as a line too, but it could happen eventually. Either that, or it could go to an online, collector-only type thing. Hasbro has sounded resistant to that in past Q and A's I think, but a property like Star Wars could probably really thrive like that (again, in the event that it couldn't make it at retail). Like it was mentioned, I would think we'd see a pretty good run through the 3D movies at least (which is near the end of the license, as of now), and beyond that we'll have to see.