What would be really important to know is whether under the RAS scheme the county council are liable for any damage done by a tenant. While not ideal if this were the situation then the landlord actually doesn't have any issue.
I've never ever heard that no ESB makes the house insurance voidable. OP is this actually in your policy?
The standard clause in a RAS lease is that the council limit their exposure to damage caused by a tenant beyond fair wear and tear to one months rent. In relation to the electricity if the Co. Co were aware that there is no electricity connected to the house they would stop paying the landlord as the house would not be complying with rental standard regulations
You need a Certificate from an electrician when the ESB is disconnected over a certain period. I think if it is over a month but not absolutely sure. It could cost about €200 plus a reconnection fee to ESB