I am not saying they will, but I don't think IOM-DUB is a key route in their network. If the PSO routes come under threat (see the current discussion), the ATR42s would probably go anyway. No need to keep one just for IOM (or are they using an ATR72 on the route ? I always thought DUB-IOM was more 19seater market than a 70seater market).
Of all the places you have mentioned, I would be very surprised if places like Carlisle or Oxford would get their first commercial route with a service to IOM. GLO serves BRS and CWL and to some extent JER, but Carlisle? Oxford - as Grater London? Hmmm. Doncaster would eat into the LBA catchment area. Prestwick - probably not viable as long as the fares to GLA are at an acceptable level. ORK sounds interesting - would there be a market?