Fedup
No one would want to buy it in its current sate. It's totally unsellable also with the market the way it is.
Do not despair. There is always someone who will buy a house in a state (I know someone who bought a "house" with no roof four years ago). At the end of the day, the land it is built on is worth a fair amount, purely because it carries planning permission for a house.
Blankface is right. A full structural survey would give you the lay of the land here. And you are going to need to don your Boudicca breast plate because with no guttering (which will require scaffolding to install), mould and rotten windows, it is going to be thousands upon thousands just to fix the bones of the house before you do anything else. But I guess you already know that deep down.
I hope, for your sake, it's not listed. If it is, in financial position you've suggested in your op, I suspect your only option would be to sell asap. I've known renovations of listed homes send wealthy people to bankruptcy.
To be honest, Fedup, I don't think this situation could have gone any other way, so don't blame yourself. You were destined to be eaten by the old house renovation monster as soon as you bought the property. As I mentioned in my previous post, because of where I grew up and live, I've known a lot of people eaten up by this devilish creature.
The only people I've ever known who have survived a similar project with their soul and marriage intact have been a) very disciplined tradesmen with a lot of cash, a lot of contacts and a tight project schedule, b) very wealthy people with a heckova of cash and a tight project schedule, or c) bespoke property developers. And by tight project schedule, we are talking about six months from start to finish.
Ime, once projects go over this kind of time frame, or you live in the property, you end up in a kind of entropic situation that requires a massive injection of energy to reverse (like a huge inheritance landing in your lap or a huge emotional shock such as a partner leaving). After ten years, I suspect you are stuck in this renovation entropy, and it's just not going to change without a massive jolt to your DH's system.
It is worth recognising that you have faced the situation by writing your post here, and I think you should give yourself a pat on the back for that alone ... because it takes courage to be honest about a shit situation like this. It is the first step to sorting it all out and moving forward. You must give yourself credit for that.