Oh, poor Rosie........I feel for you.

I did a similar thing the other day in Photoshop. Was working on a very complicated texture, with loads of layers, turned the most salient one to grey scale to check the bump mapping and accidently hit the save button. Fortunately I had a jpg saved of the original, but can't tweak it any more.

Hope you have a good new year, apart from that.

The greatest part of wisdom is learning to develop  the ineffable genius of extracting the "neither here nor there" out of any situation...."