If William the Conqueror is to the Roman de Rou what Arthur is to the Roman de Brut, we would expect his highpoint to be followed by a pattern of decline. This is indeed what happens, but in such a different way to what we find in the Roman de Brut that the comparison is barely valid. Contrary to Arthur, William is a deeply flawed character, from whom much of the darkness in the ensuing narrative originates; his failure to follow in the footsteps of his wiser forebears and forego the royal dignity results in an identity crisis in the ducal family and leads to internecine warfare. The narrative ends with the demise of the last duke of Normandy (as opposed to duke-king), Robert Curthose, at the hands of his younger brother, King Henry I of England. There is more to this final section of the Roman de Rou than meets the eye. While Wace refrains from overtly commenting on the issues that arise in the wake of the merger of England and Normandy, we find echoes from earlier episodes in the work that give strong indications as to the poet's views. The final 1600-odd lines of the work are thus highly politicised, albeit in a relatively discreet way.

The aftermath of Hastings is both violent and unpleasant in the Roman de Rou, with Normandy apparently treated in a way not dissimilar to England by the victorious duke (9011–18):

The impression given by these lines is that William's grasp over Normandy is as insecure as it is over England, with the stress put on the punitive aspect of his visit. Whilst the quelling of robbery and thieving (‘larrons’) is entirely laudable, the mention of ‘felons’, which can mean ‘traitors’ as well as ‘criminals’, suggests an undercurrent of feudal revolt by nobles trying to take advantage of their lord's protracted absence, and therefore a breakdown in law and order due directly to the English campaign.