It'll be interesting to see which routes Ryanair bring back, and whether they decide to try any that they haven't had a go at before.
Between 2005 and 2008 Ryanair tried just about every route imaginable, before binning the vast majority of them and cutting the base back to the current list: Alicante, Lanzarote, Liverpool, Gatwick, Stansted, Malaga, Nantes, Palma, Tenerife and Wroclaw.
At the peak in 2008, Ryanair was flying 20 departures a day with 6 based aircraft, compared to only 5 daily departures and one aircraft now. They should have data about which routes (if any) were profitable, which should allow them to avoid the risk of trying untested routes.
Here's the list of dropped routes (I may have missed a few as there are so many):
Beauvais, Bergamo, Birmingham, Biarritz, Bournemouth, Bristol, Carcassonne, Rome Ciampino, Charleroi, Dublin, East Midlands, Edinburgh, Faro, Fuerteventura, Gdansk, Girona, Hahn, Krakow, Katowice, Kaunas, Leeds Bradford, Lubeck, Lodz, Luton, Madrid, Manchester, Murcia, Newcastle, Niederrhein, Skavsta, Prestwick, Riga, Berlin SXF, Turin, Treviso.
FR said there SNN base wasn't viable before the major reduction so this time they will go for targets they can meet.
Routes that I think will return will be:
Milan BGY
Paris BVA
Barcelona (GRO or BCN)
Brussels CRL
Krakow
Bristol
Frankfurt
Possible somewhere else in south France and another Polish.
They will increase flights to Malaga, London, Liverpool, Palma.
Big question is will they be able to resist SNN-FAO route if they start it Aer Lingus will drop it (good news for ORK) and Brussels is very possibly and this could also affect EI at ORK.
It hard to call as a spate of touristy routes from both ORK and SNN won't work long term that's if ORK will get something from this but if they directly or indirectly target EI/EIR it could be good for ORK as EI will leave.
As you say they have tried just about every route possible so they will most likely stick to what was somewhat viable as going to those places that failed in the good times now would just be poor management.