Effortless: I am not an expert in this field, but it seems to me that if the company has gone into administration, it doesn't mean that the company no longer exists. It means that the company is not being run by its previous managers, but is being run by the administrator instead. He can determine whether the aerodrome is open or not, as he is (effectively) the licence holder.
So if he has determined that Shoreham is closed, then closed it is. Mind you, there is a regulation that states that an aerodrome cannot be closed unless essential services are not available, but that only applies to Public Use licensed aerodromes. Those with Ordinary licences can close down whenever they feel like it. There are not many "essential services" required for a small private aircraft.
If the aerodrome operating company had gone belly up, and the aerordrome was floudering around without any owner or lessee (but presumably the local authority still retains actual ownership?), then I guess the aerodrome would be the equivalent of a grass field, and you could take off without having to get anyone's permission.
If I wanted to get my aircraft out of Shoreham, I think I'd just go, and argue afterwards. I can't see that I would have broken any law unless someone in authority had expressly told me I could not take off.