I cannot repeat often enough that I am well aware that the existing ending does NOT suggest any of the Gang died or the Great Valley being anything but a real place which one could see with the eyes just as well as with the heart if the eyes happened to be in the vicinity.
It also is quite clear that if there was an alternative concept it must have been abandoned relatively quickly (just think of the original plot of Littlefoot leading the others to the Great Valley after he found it but decided not to enter without them. If the Great Valley had at that time still been interpreted as a dinosaur heaven that would be kind of... morbid?). For the same reason all we do see in the movie (absence of characters like Littlefoot's mother (though one could point out that of all possibilities it was her ghost leading him on the last steps)) is definitely on the assumption of the Great Valley being a very real place.
I cannot stress it often enough, in the movie as we know it the Great Valley is
NOT a dinosaur heaven and
none of the characters did die. All that I consider quite possible is that at an early planning stage there may well have been such a concept in the minds of the movie makers, a concept though that was quickly abandoned. Still some of the elements of that concept may have made it into the movie because "Some things you see with your eyes, others you see with your heart" of course sounds a lot better than "Grandpa told me"
