Will they be ruined by the Sun, or preserved by vacuum?
Probably faded to white from intense UV. Not sure what the physical condition of the paper would be, but I’d bet it would be crumbled to dust by now from the temperature changes alone. If he’d tucked it into a rock’s permanent shadow, it could have lasted hundreds of years or more. But exposed to the sun… it’s toast.
Wasn’t a letter or a book or something left behind on a lunar mission the maguffin in Space Cowboys? Or was that Homer Hickam’s novel?