The issue of Beowulf's men failing to come to his aid is complicated by the speech he gave to them just before he entered the dragon's cave:
You wait on the hill, protected by war-mail,/men at arms, to see whether one/of us is better at surviving his wounds/ . . . It's not your duty,/nor the mandate of men . . . to expend energy against the monster. . . .(ll. 2529-2534)
Beowulf, knowing that this battle is his last chance for personal glory and, more important, perhaps the only opportunity to save his kingdom from the wrath of the dragon, essentially orders his warriors to stay out of the battle. Under other circumstances, Beowulf's warriors would be expected to support him, as they had done many times during Beowulf's kingship.
The problem, of course, is that Beowulf's men obeyed him to the letter, and the culture to which these men belonged did not allow a leader's men to abandon him under any circumstances:
His right-hand men, those sons of princes,/didn't stand by him . . . like decent warriors, but fled to the wood/to save their lives. (ll. 2596-2599)
Despite the fact that Beowulf tells them to stay out of this fight, his men understand that if their leader is clearly in jeopardy of losing his life they are bound by the bonds of loyalty to enter to battle even if they think they may not survive. In a culture in which loyalty and bravery in war is everything, they fail in two very important ways: they abandoned their king and they showed cowardice.
The saving grace in Beowulf's last battle, however, is the loyalty demonstrated by the youngest warrior, Wiglaf,
. . . could not hold back, his had seized his shield,/the yellow limewood, he drew an ancient sword. . . .(ll.2609-2610)
He then addresses the other warriors and reminds them of their duty--despite what Beowulf has told them--to support their king, who has shown them nothing but kindness and generosity. Wiglaf's speech, unfortunately, has no effect on the rest of the warriors, and he goes to Beowulf's aid alone.
Beowulf's cowardly retainers suffer the greatest punishment this culture can provide--they are forevever banned from Geat society; they and their families are stripped of their land; and they are forever branded as cowards.
The kingdom, however, has a new leader, Wiglaf, who carries out his duty as Beowulf's retainer despite his youth and inexperience--and doing so with every expectation that he will not survive. In a culture that honors loyalty, bravery, and fighting prowess above all else, Wiglaf rightfully steps into Beowulf's position as leader of the Geats, and so there is every reason to believe that the Geats, under Wiglaf's leadership, will survive and prosper as they did under Beowulf's kingship