As far a UK taxpayer goes it would be better that FR runs less flights. Ryanair pays no tax in the UK and most of the pax in winter are taking money out of the UK to spend somewhere warmer. It is simple that holiday locations need low airport taxes to get the pax to come but the UK gains from higher airport taxes.
The real killer will be when the EU has a EU wide common tax at around 20 euros per departure.
The other issue is that ryanair hedge about 90% of there fuel requirements. The profitablity of the last 10% of flying will depend on the spot price for fuel.