I'm so pleased that you've got your cat home safely. There are some horrible posts on both threads, but I suppose it's no more than I would expect to see on Mumsnet. I've followed your threads since your first post yesterday, and I don't think there's any more you could have done, despite the repeated posts giving you exactly the same advice, often from people who clearly haven't read the threads.
The most important thing is that your cat is safe. If the house is currently being renovated, I would think it's unlikely that the rug is new and there's nothing to say that it's an expensive one anyway. Your cat probably hasn't done many wees in the house as he wasn't taking in much fluid so hopefully he's only used the one area, and if it's just gone onto the floorboards, I'm sure the cleaning products that other people have provided links to will work. The crab sticks may smell a bit by tomorrow, but the smell with be gone in a few minutes with the windows open. I wonder if you could try to catch the builders at 8 when they arrive in the morning and ask them to remove the crab sticks and ham, and open the windows, then hopefully the house will be smell free when the owners arrive. If they've got a long journey they're not likely to be there too early. I also wouldn't worry to much about the scratches that the cat made trying to get out - it's unlikely that it will need more than a bit of poly filler and a couple of coats of emulsion.