I don't think there's any contractual agreement to never release the OOT until after Lucas' death. It'd be a very odd and uncomfortable discussion to have at a business meeting and frankly just doesn't make sense given the fact that Lucas approved the release of the GOUT.

I also don't understand the argument that Disney will interfere in the home video releases of Star Wars films. Lucasfilm still exists as an entity. Disney didn't buy Star Wars, they bought Lucasfilm, and everything it owned, which includes Star Wars. Lucasfilm is, to a certain extent, an individual company with it's own managers and producers that Disney ultimately has control over. Of course Disney could make them do whatever they see fit, but the idea of really high up Disney executives shutting down, or even caring about, the home video releases of old Star Wars movies is a bit far fetched I think, especially given that the real focus is no doubt on the new movies.