Given that quite a few destinations from Northern Ireland, Isle of Man or the Channel Islands have will in excess of 120,000 (with some being more than 240,000) passengers a year then that's enough to have between 80 to 160 passengers on two flights a day in each direction, then there's likely to be demand.
As such then there's a chance that someone else will offer the route. It would lead to a smaller choice of where you could fly direct between, however do we really need to keep open routes which run with fairly few people. Do we, as an example, need a flight between Stansted and Newquay which has 5,500 passengers a year? If we do how about Newcastle to Newquay which is sub 2,000 a year?
To be viable either the frequency is very low or the flights aren't just between those two points.
I don't know when either of those last ran, or if it was Flybe that did it, but Newquay doesn't have regular flights to either Stansted or Newcastle right now.
If a route can fill a regular flight by Flybe that doesn't mean it will be picked up by any other airline - Easyjet might offer a decent number of domestic flights, but regular flights between regional airports are for the most part not their business and they've got at least 150 seats to fill on each plane, Loganair I doubt are capable of expanding to take any notable number of Flybe's passengers. In the short term though there aren't likely to be takers for many, or any, routes, regardless of how busy they are, because other airlines have already sold tickets on every plane they have to go somewhere else this summer. Unlike a Thomas Cook holiday destination temporarily disappearing, that's a big inconvenience (and political headache for the government) particularly for the islands, Northern Ireland, and the various airports that might not still exist by the time someone wants to fly there.