I believe Lucas will not run this thing into the ground. Some people criticize him for the StarWars prequels and they have good points for it, they are seriously lacking on some of the ingredients that made for the originals. Some might say Lucas lost his touch, his magic.
Well, the thing is, George Lucas is just what he is, a visionary, a thinker, the man who pops "super ideas" out of his head. The problem is he is not a genius, like Spielberg his, in his own admission to this, he said about doing Indy4 and SW at the same time something like "I can't do multiple things at once, I'm not Steven, I have to take one thing at a time."
So, he's a wonderful story teller, a "huh, great, print it" director, and a very good editor. He just sucks at screen play writing, he can't help it, we all suck more at some things than others, but most of all the man did not improved this craft, this skill, the last screenplay he wrote before SW1 was back in late 70's. In short, he lacks in execution of what he excels in imagination.
With Indy4 we have it all, what I like to call the creative quartet "Steven Spielberg at the geniality, George Lucas at the vision, Harrison Ford at the charisma, and John Williams at the heart."
So, Long live all of them, Long Live the creative quartet, and by god, Long Live INDIANA JONES 4!!!