I'm not so sure how much ILM and Skywalker Sound have to with Lucasfilm as far as if one went under the other would survive,

But hasn't Lucas said that no more films will be made after his death? I can't imagine Lucasfilm won't continue with cartoons, tv shows, novels and comics ie the expanded universe. And I can't imagine Lucas caring that this continues after his passing, just like he doesn't have a problem with it now.

All that ancillary stuff is fodder for more merchandise. From what I understand The Lego Star Wars range is predominately Clone Wars orientated and is doing quite well. Who needs films to sell toys?