Until Aer Lingus decide to scale up ops at Manchester, there will always be a risk of issues like this happening. Even with 2 A330s planned next summer, they'll be both working the daily JFK and MCO services so there still won't be any slack in the schedule or spares available. The fact they chose not hire in capacity for the week probably suggests it was easier to rebook passengers on BA/VS and their own services via Dublin.
The A330 winter maintenance has started as well so there may not have been available capacity to take from Dublin with a busy schedule still operating. How they'll cover G-EILA's scheduled maintenance this winter will be interesting!