I happen to remember where I was when Superman "died." As a teenager, I was at a planning meeting for an organization I was involved in, and as it broke up, somebody noticed that it was past midnight, and thus the day of Superman's death had arrived.
Not being a Superman fan specifically, I had been generally aware the the death of the Man of Steel was coming up, but I didn't know anything else beyond that. It was not until about a year or so later that I read the Death of Superman collection that followed his running battle with Doomsday. However, as our meeting was breaking up, there was suddenly a great deal of discussion about the big comic event that day. I got the impression that there was to have been some kind of midnight promotion event, but I am not sure what form it might have taken. (This was a bit before midnight premieres for highly anticipated movies, which seem to have begun in earnest with the Star Wars re-releases a few years later.) So was it just that comic book stores were going to be open at midnight to start selling Superman #75 that night, or was there a more elaborate midnight promotion?