I think we can assume that Beowulf's cause of death in the great saga was that as a result of the epic battle with the monster, he bled to death. The whole story-poem is full of blood-thirsty and blood-letting incidents and references right from the start, so in a way it is telling that this is the way that the great hero Beowulf is himself going to die, a foreshadowing. In the Christian story we have the image of Jesus dying on the cross and losing blood. Beowulf sacrificed his life to defeat the monster, but did he have other motives? Was he too proud to accept help, or to compromise? Did he have an ulterior individual motive of ego and pride as well? Certainly this possiblity did not worry his distraught followers - they "rode around the barrow to make a lament" and they "lauded his reign and praised his feats of prowess" but was he "the most eager for praise" to an extreme degree?
In the epic Old English poem Beowulf, Beowulf is a heroic warrior who battles Grendel, a golem like creature. He goes on to have his own kingdom for years but a dragon comes to destroy it. Beowulf takes his men and goes against the dragon. The dragons flames beat him back at first. Beowulf raises his shield to protect himself from the dragon. He stabs the dragon with his sword. However, the dragon remains strong. Beowulfs sword has failed him. He is surrounded by the dragons fire and his men desert him. In Episode 11 he fights the beast. Wiglaf returns to help Beowulf. Beowulf again tries to stab the dragon but his sword breaks. Then the dragon bites him. He pulls out a knife and slits the beast down is belly and kills the dragon. He dies from the wounds.
He bit Beowulf's neck
with sharp tusks--Beowulf
was wet with life's blood;
blood gushed in waves.
Beowulf is seriously injured in Episode 12 he dies and leaves his rights to throne to Wiglaf.