The failure of comitatus at the end of the poem is seen in?The poem is Beowulf.
Comitatus is a germanic warrior bond, or simply, an honor-code among warriors to fight loyally (committedly). The agreement was that the lord or king offers protecion for his thanes (warriors, usually of high position) and offers them a share of the riches and treasures (sometimes even land). In return, they pledge to fight to the death for him.
At the end of the story, Beowulf is up against the dragon alone. His men are nowhere to be found when he clearly needs help.
There are to other thanes whom Wiglaf (one who has been with Beowulf from the very beginning) calls together at the end to remind them of their commitment to Beowulf. He is attempting to shame them into fighting the dragon with him. He even says, of himself, he'd rather be burned to death than abandon his king. None listen. Wiglaf enters the battle with Beowulf, and ends up succeeding, though Beowulf is mortally wounded. In the end, Beowulf thanks Wiglaf by making him his successor. Therefore, Wiglaf has earned rather than inherited the throne.
The failure of comitatus therefore, is seen in all of Beowulf's men except Wiglaf.