I think that that would be very callous of them to do, frankly. This is someone that Universal respects immensely because his movies are often associated with them, and because they made them lots and lots of money. To be waiting for him to pass so they can say, “oh, sad...anyway!”, does not add up for me.
On top of that, I’m sure that, if his wish truly is that E.T. not be replaced (which may not be so, as Alicia says), his family would put a stop to it, and if not them, either personnel from Amblin or the likes of Kathleen Kennedy would have something to say.