I don't think the so-called demesne could last long : it was too divided, too threatened to survive on its own, save a collapse of its neighbours.
Not only Franks would still dominate Belgica (Clovis being only one of Frankish kings) and Germanica, but you already had several Franks in this region (descendents of laeti or from barbarians general of roman armies as Abrogast).
The militias and armies were composed of various peoples as such, and the division of the demesne among fifferent counts greatly helped Clovis OTL ( Arbogast, Syagrius, Paulus, etc.)
Adding to likely incursions from Franks, Thuringii, Alemani an Bretons are also to be considered.
Futhermore, the growing influence of Visigoth in Northern Gaul would be the last drop : alredy important OTL, and unchallenged ITTL, it could lead to its absorption (as Auvergne was) or at best, a visigothic overlordship.
Syagrii family was, after all, widespread in their kingdom, and part of their court.