I suspect Loganair or Blue island as already said would be interesting in filling the hole for Jersey.
Jet2 already fly to BCN, NCE and GVA from other UK bases so would potentially be a candidate for those routes, with BCN and NCE probably fitting quite well into their city breaks brand.
The remainder of the capacity to places like ALC, AGP etc would probably in normal times ended up being divided up between TUI, Jet2 and maybe Ryanair, but at the present time there probably isn’t the demand for these airlines to fill their already scheduled flights so I can’t see them adding any more capacity.