Aer Lingus are trying to operate in a very challenging environment (deeper felt in Ireland) and it hasn't been able to spread risk like others.
Aer Lingus has positive brand recognition so if the opportunities exist elsewhere (and they have key competitive positions in LHR) then it is the shareholders who call the shots. Go for it Aer Lingus! Antitrust concerns will protect you.
What would happen the island of Ireland if there was only one operator. Don't people ask why is Aer Lingus important to Ireland?