The sad event that concludes the epic is the elderly Beowulf’s death in the battle with the fire-drake.
At the beginning of the tale, Beowulf is a strapping young man in the prime of youth. He is already a hero, and has come to fight the monster Grendel. His men follow him unquestioningly, and Hrothgar welcomes him with open arms to take care of their resident beast.
Beowulf does so, and very successfully. He kills Grendel and Grendel’s mother, following the latter deep under the earth. He is able to retire to a life of relative leisure at home, until a new threat emerges.
Beowulf leaves the fire-drake a “fearsome and grisly fiend, all scorched with flames.”
It was fifty foot-measurements in length where it lay. It had been supreme when it went aloft during the night-hours, then returning back to seek its den—now in death's fast clutches it had ended its joy in the earthen caverns. (Ch. 41)
Beowulf started out fighting it with an army, but soon Wiglaf was the only one left. With no weapon but a dagger, Beowulf killed the dragon, but he was mortally wounded in the process and did not live as long.
After “fifty winters” (Ch. 37), of peaceful rule Beowulf had more than earned retirement. His honor would not allow him to think of it. He died a hero’s death, and saved his people.
Most epics did end with the hero’s death, often in battle. After all, how could a hero just die of old age? He has to go out with a bang, in a blaze of glory, as a hero should.