IAG will efficetively shut down all transfer traffic from the Uk-Us via Dublin. The hub status that Dublin is hoping to achieve would be no longer possible and EI would probably pull out of Shannon and Cork.
Not so sure...DUB might be an enticing option for UK regions to the US, and BA might well support that. If it takes some pressure off the LHR operation, it could be beneficial for BA. I actually think EI in IAG would be in a healthy position...finally having the protection and resources of a big group, and possibly playing a key role in that group via DUB.