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.

After Beowulf slays Grendel and Grendel's mother, he returns to Geatland (modern day Sweden). His lord, Hygelac, and Hygelac's son eventually die, leaving the crown to Beowulf. After ruling for five decades, a slave awakens a dragon and steals some of the dragon's treasure. Angered at this, the dragon attacks the Geats. Rather than risk more lives, Beowulf endeavors to fight the dragon himself. However, Beowulf is accompanied by some of his soldiers. When they face the dragon, all the soldiers flee except Wiglaf. Together, Wiglaf and Beowulf slay the dragon, but Beowulf is mortally wounded in the fight. 

The epic ends with Beowulf's funeral. Wiglaf and Beowulf's company go to Earnaness, which is the headland where Beowulf fought the dragon. They push the dragon over the cliff into the sea. They make a glorious funeral pyre for Beowulf, adding treasure from the dragon's lair. They mourn the loss of their king and fear that foreign armies might attack when they learn that their great leader has died: 

Sad in spirit they lamented their heart-care, the death of their liege lord. [And the Geatish woman, wavy-haired, sang a sorrowful song about Beowulf, said] again and again that she sorely feared for herself the invasion of armies, many slaughters, terror of troops, humiliation, and captivity. Heaven swallowed the smoke. 

Lastly, they build a monument for Beowulf surrounding the remains of the funeral pyre. 

The sad scene that concludes this epic is Beowulf's death.  A dragon is threatening the land and he and his men go off to fight it. Beuwolf senses that his time for death is near, and begins reflecting on his life while sitting on the cliffs. He talks about his grandfather and how his grandfather was stricken with sorrow over the death of his oldest son. Beowulf also talks about his ventures in warfare and reflects on his loyalty to his Uncle Hygelac, as well as defeating the champion of the Franks on his own. On this note, Beowulf announces that he will fight the dragon alone.

However, Beowulf is not able to kill the dragon. One of his young warriors named Wiglaf comes to help him and they kill the dragon together. However, Beowulf succumbs to his injuries. Before he dies, he thanks God for his life and asks Wiglaf to take care of the Geats. He also asks that a barrow be built on the cliffs in his memory. The epic ends with the Geats gathering around the barrow and mourning their king, Beuwolf.