I think its fairly clear that Lucas(the 'Evil One') clearly had the re-write done to provide a 'jumping off point' for further movies and to keep the franchise going. There will I think be an 'Indy 5' in some way or form.
Remember the ideas they shelved from Raiders and later used in TOD?, I think we'll see the plane chase turn up in the next installment.
I hope too Marion will be there with more to do.
I agree that there are weak elements to both Koepp's and Darabont's scripts and strenghts too.
I do think Darabont SHOULD have recieved some credit for his work in some way.
I think there probrably working on a script now as we 'speak'.