Rindercella - And people routinely drive their children along A roads / dual carriageways (the most dangerous roads in our country, I think?) for non-essential purposes. To go and buy wine, even, or visit friends, or those other little things that people do for non-essential pleasure. Push your baby across a busy junction in a buggy to buy cigarettes? Take your baby in pushchair along a pavement on a windy county road along which cars speed and may mount the pavement to go to the shop for bread milk, or god forbid a bottle of Lambrini? Perfectly normal behaviour.
The 'risk mitigation' that the OPs DH did no doubt included clocking that the toddler was a) asleep in a cot which b) he cannot get out of. I doubt he would have nipped to the shop had the toddler being toddling around in the kitchen, while he went of for his non-essential pleasure be it cider, mars bar or fanta.
This situation seems to have become a magnet for everyone's projected issues. SS will take the child away? Amidst loads of posters claiming that they would break up the family and the bond between a child and it's father as the best outcome of this situation. Is any of that REALLY in the best interests of the child?
Of course SS will not take a child who is fit, well, happy, clothed, fed, not bruised or bashed because it was left asleep in a cot for 5 mons. Not a child of any description.