Bit of an update. Casper came home from the vets this afternoon, he is all settled in to Lesleys cage (thank you so much Lesley!) and seems to like the girls heated bed so much that he will be keeping it for the time being if not for good, they don't seem to use it much anymore, our bed is much better!
When I first saw him, he was lying doen on the bed and although half of his back end is bald and the wound is huge, it didn't seem so bad. Then he tried to stand up, he did surprisingly well really, apart from a bit of a wobble where he tried to put down the leg he no longer has, he managed to hop to the other side of the cage and lie down near the bars so I could fuss him. I was rather shocked when he stood up though, I hadn't really thought about how much of the side of a cat is leg bone and it brought tears to my eyes to watch him trying to move, I feel so sorry for him as he must have no idea what is going on at the moment.
Apparently at the vets just before mum brought him home, he had a panic attack, falling against the cage, thrashing his remaining legs and growling. The nurse said it had happened a few times and it was very distressing to watch so we're really hoping it was a smell wafting past or something unfamilier that spooked him as I can't imagine having to watch him like that. Luckily he doesn't seem to be in any pain but we've got the metacam to thank for that.
I guess we have to see what the next few days bring.