Hi!
As for the dinosaur in the story Littlefoot's grandpa told, I'm convinced that what we saw was the way Littlefoot imagined the story he was just hearing. If they had made that lone dinosaur look different from Doc nobody would really consider them to be one and the same.
I don't really believe in ghost stories in the land before time, ghost stories that go beyond what we saw of Littlefoot's mother that is. Still I do think that Doc MAY be the lone dinosaur.
This may sound like an antithesis, but in fact it isn't. There is one factor that mustn't be neglected. The story of the lone dinosaur is a LEGEND. This means that the story of something that has actually happened has been told and re-told many times and many of those who told the story may have added their own little details.
So actually Doc may be a dinosaur who defeated a sharptooth long ago. Many dinosaurs in the land before time did the same. Perhaps it was Doc's striving for solitude that caused this story to be especially embroidered. The only difficult point is that from what he says Littlefoot's grandpa heard this story from his own grandpa. This would probably make Doc too old so he may just resemble (the scar and his abilities) the longneck who defeated a sharptooth in the Great Valley long ago.
I do not think that Doc was a ghost.
As for his disappearance, it may again be that it was Littlefoot's phantasy, or perhaps it was caused by a mirrage of the setting sun.
What I like about the story of the lond dinosaur is that everyone can interpret it for him or herself. Nobody is forced to believe in ghosts, but anyone who wants to can do so. I regret that they didn't keep up the same kind of mysteriousness for the rainbowfaces in LBT 7.
