It's certainly a major concern for Knock.
FlyBe were responsible for 14% of all passengers at the airport in 2018. Only Belfast City is worse affected in Ireland as a whole, while south of the border, Dublin (1%), Cork (0.4%), Shannon (0%) and Kerry (0%) will see very little impact.
It could be an issue to attract in another carrier, with Ryanair flying to Liverpool and East Midlands, and Edinburgh the most marginal of the three. There aren't many carriers around these islands with the right equipment for the routes either.
A best bet may be Stobart/Aer Lingus Regional, but that would imply plenty of Ws, unless they could be persuaded to actually base an aircraft in Knock. At the moment, they have 5 aircraft dedicated to FlyBe and the wet-leased ATR72 could probably be pretty quickly repurposed.