Understandably there is huge speculation about what IAG would do with EI's operation, e.g. curtail the scale of US routes and channel through London.
IAG clearly are interested in EI, and the future viability of EI operations are through an increased transatlantic operation at Dublin which will ensure that the short haul operation is sustainable, which Ryanair is all over and will be more so in future.
Moving away from the core strenght and profit generator that is North America would spell doom for EI, and leave it completely exposed to Ryanairs point to point business.
There is a much bigger world outside of EI and if IAG want to secure EI to drive their London TA business etc. there are lots of other carriers who will fill the voids ex Dublin.
EI-BUD