Well I think you said it really, things still being live when you think you switched them off. The other main possibility is damaging equipment. It is one of the primary tests and it is unthinkable that it was left out by some one. This is gross negligence.
In Tort there are three hurdles to claiming damages. One, was there a duty of care? Absolutely-Two was the duty of care breached? clearly it was-And three did any harm result from it? No.
However had your Husband decided to sink a socket and was not competent electrically he may have been electrocuted. If he undertook work he was not competent to do then and harm resulted that would count as contributory negligence.
I think you have had a very lucky escape. Give thanks no harm resulted from this.