Time travel in superhero comics is often a protective measure undertaken by heroes, a utilitarian effort in order to ensure the safety of a future status quo. This idea presents time travel as a protection of fixed points in time that must remain unchanged. You can play with the point, but you cannot change what has to happen, and it usually is a monumental event of some type. For the creative team of Morrison and Quitely it is a death that is a fixed point, and the need to recognize mortality as necessary in the time travel comics narrative proves to be one of depth and dramatic weight in the hands of these creators.
There are a number of events that must occur for Superman in the larger structure of Morrison’s twelve part “All-Star” story. These events are the twelve labors, or impossible feats. Superman is motivated to undergo these labors as he is quickly dying from massive cell degeneration brought on by overexposure to the radiation of the sun in issue one. One of the labors turns out to be joining forces with other generations of supermen to defeat the chronovore, a 5-D being, a “time tornado” aging and dessicating everything in its path. These other generations of Supermen are apart of a self proclaimed “Superman squad”, who “have banded together to defend the time stream”.
The chronovore is not the most important thing here, and it is a bit of misdirection that Morrison pulls in his script. As the battle is fought in one part of Smallville, Clark Kent’s adopted agrarian hometown, Jonathan Kent dies quietly in a field of a heart attack. Natural death is the one thing that superman can not beat—superman can not, for all his powers, defeat time. Superman’s solution, and Morrison’s in acknowledging that Superman has often time traveled, for defeating time is to manipulate it to provide him closure. As the story is set in the “past” of the main narrative, “future” Superman decides to disguise himself in bandages, join forces with the supermen of the future, and returns to the battle of the chronovore in order to spend a precious few moments with Jonathan Kent before he dies. But why not stop the event?
Stopping the event would upset a “fixed point” that I mentioned earlier, that event that must always happen in order for other important events to come to fruition. As one of the Superman squad reminds the reader, Kent’s death is a catalyst for other necessary events to occur, most of them we must believe to be in order to do good or to defeat evil (in thinking about comic genre narrative devices), but none of that can happen unless first Jonathan Kent dies in order to get Clark Kent/Superman out of Smallville to embrace his destiny. Therefore, Morrison and Quitely use the fixed point idea of time travel to illustrate the importance and necessity of mortality, an emotional element that can be overlooked in time travel narratives in comics.