The Internet is full of lies... and myths about comics
Many people claim that in the Death of Superman story that Superman didn't die, but instead fell into a "healing coma."
BACKGROUNDIn 1992 DC Comics announced that Superman was going to die in an upcoming issue of Superman. It made headlines across the world, and was bigger news than even DC expected and they knew it was going to be big news.
The 90s were known as a boom decade for comics, with a strong presence in the market of speculators, people buying comics as a collectible investment, for future sales values rather than to read: X-Men (vol 2) #1 released in 1991 had become the biggest selling comic of all time, which rumours that some people were buying 3 issues each.
Although Superman's fight with Doomsday (the creature who killed him) lasted 7 issues and appeared in 5 different comic book titles, the issue in which Superman actually died - Superman (vol 2) #75 became the biggest selling non-first isssue ever, over 3 million issues, and was the biggest selling comic of 1992. The next most successful Superman comic that year, the issue before Superman #75 in the fight, Superman: The Man of Steel #19 came in as 109.
Death in comics hardly ever lasts, and the death of Superman was shorter than most, and many were upset and felt cheated when he returned from the dead about a year later. And the method of return lead some to say he didn't die, but just went into a "healing coma."
When Superman and Doomsday killed each other, Superman appeared dead and was given a funeral and buried. Clark Kent's foster father, Jonathon had a heart attack and, in the afterlife his soul met Clark's trying to enter the afterlife. Both souls returned to their bodies...
Then four replacements appeared. One of which dubbed "The Last Son of Krypton" turned out to be the disembodied Kryptonian AI "The Eradicator" who, on discovering that Superman was dead, attempted to enter and steal Superman's body, which had, due to its Kryptonian physiology remained intact. Unfortunately for the Eradicator, Superman's soul had returned to the body and he placed the Kryptonian Regeneration Matrix in Superman's Fortress of Solitude. The Eradicator then created a new flawed body to inhabit. The matrix restored Superman to health (but not to full power). Soon after the Eradicator used the Regeneration Matrix himself, destroying it.
Then nature of fiction is it is infinitely interpretable, so yes, that could be considered death and resurrection or it could be considered a coma. Maybe Jonathon only imagined meeting Clark in the afterlife. Maybe Superman was still "alive" and the Eradicator didn't know it. Maybe, And maybe not.
The Eradicator was a device that had a history of manipulating Kryptonian genetics. If there is any being to be considered an expert on Kryptonian physiology, it is the Eradicator.
In Superman (vol 2) #82 the Eradicator explains to a still confused and recently resurrected Superman that he had in fact died. In the pages he specifically discounts the notion (presented here by Superman himself) that Superman was only in a coma.
This still doesn't say for sure that Superman was dead, but it does discount the theory some have that Superman has some previously unknown sort of resurrection power or immortality.
Like most super hero universes, the DC Universe has its share of supernatural characters, and some of them had something to say about Superman's death.
In The Adventures of Superman #692 Lois questions whether Clark is immortal, leading supernatural detective Doctor Occult to appear and tell them that Superman definitely died.
In 2001, the mini-series Deadman: Dead Again featured Deadman (a ghostly superhero) attempting to stop Darius Caldera (a wizard who uses souls) and Neron (a demon) from collecting the souls of dead heroes to perform a ritual. In it they attempted to capture Superman's soul when he died, but capture Deadman instead.
So with at least four experts on souls and the supernatural believing Superman was dead, it's pretty safe to say that, yes, he was dead.
While it is clear that the comics meant for Superman to be dead, nothing will change the real reason for the "healing coma" theory. Some people just feel ripped off by Superman returning for the dead. For these people, Superman's temporary death was a cheat and the exaggeration "healing coma" is just their way of venting.