Providing they keep costs down, keep fare differentials between themselves & their competitors high (to compensate for non-central airport usage), don't crash, and the EU don't rule illegal/unfair subsidies that FR get from various regional authorities - (to be fair, the subsidies are not exclusive to Ryanair, it's just that other low-cos would rather not compete at the same airports), and regional authorities all over Europe have subsidised non-aviation related industries to locate in socio-economically (& geographically) marginal locations - they should be fine.