VLM generally carry 20-30 pax on the JER-LCY service; not a massive load but their fares aren't overly cheap, especially for last minute bookings which is what the vast majority of bookings are.
Either way I doubt they'll carry on with the service when VLM get completely absorbed into AF/CityJet; I'm sure they won't take too kindly to an a/c sat in Jersey all day with an 'on duty' crew in a hotel.
I think a GCI-JER-LCY rotation would work, especially if VG/AF can the current service. Although not the direct link that Guernsey pax would prefer, it would make the service much more viable.
Is there potential LCY slot availability though to allow the service to operate at sensible times?