Gran Canaria & Fuerteventura must surely be routes which are ripe for take over from Ryanair by another carrier?
Both Monarch & easyJet have plenty of flexibility in their winter schedules so perhaps one of them will take these on before too long.
Does the fact Ryanair are quitting these routes mean they are reducing capacity at Luton or could new routes or frequencies be added? I'm surprised, given how popular it is, that Dublin isn't at least 4x daily?