It would be nice to think Ryanair might up service to Gatwick, but I can't see it happening.
What if Aer Lingus don't get the slot at Heathrow? Do they retain Gatwick?
There are a very small number of slots freely available at Heathrow without having to indulge in trading. Mostly, they are not ones an airline would want (e.g. a late arrival and early departure that would cause overnighting and the need for 2 crews), but if I read them correctly, there is one available with an arrival into Heathrow just before 7pm and departure just before 8pm that could be worked with. Although, that would leave the aircraft back in Cork quite early, but late enough that it couldn't be used again that evening.