While I do remember the remake using the death motif several times more than the original, and listening to the soundtrack seems to confirm it, I also can't help but feel that the remake used this motif as a story telling crutch due to the difficulty in expressing emotion with the realistic CGI. When you can't show Simba being upset, simply play it and the audience hears that they need to feel upset.
And yes, Mozart can be heard several times in
The Lion King's score. Mufasa's death motif as well as the first part of the standard soundtrack's
Under the Stars come to mind.
Without re-watching the original movie, I seem to recall three places where the death motif shows up: the first time after Mufasa's death when Simba finds his body, the second at the mystical pond/spring with Rafiki right before Mufasa's ghost, and pretty soon after that again right after
Busa when Simba returns to his ruined home.
My favorite version is this second part at the pool, although perhaps it's also because it's my favorite scene in the whole movie (and no, I actually don't include Mufasa's ghost as part of that scene). While the remake used a rather obvious alpha-blend (IMO) to switch between Simba's reflection with that of Mufasa's, I just checked in the original and it used a much simpler trick: it cut to Simba's face to hide the switching of reflections.
This caused me to realize: Quite a number of times in the original, all we see occupying a good 75-90% of the screen is occupied by a character's face. And yet this cartoony art-style was able to show the emotions going through the character and help tell the story that way. Back to the reflection scene: We don't see the reflections change: the first cut shows to Simba, the next time we see the reflection, it's Mufasa. But between that, we see Simba reacting to
him seeing the reflections change, and I think it hides the fact that the animators couldn't figure out how to swap the reflections in real-time. But we don't need to see them change: Simba's expression tells us everything.
Okay, yes the music helps a lot, but in the original it's my favorite scene. In the remake, especially with that alpha-blend... it felt rather
narmy.