A copy of the painting can serve for viewing nearly as well as the original. But a copy can’t answer some questions so preserving the original for future study (and new questions, ideas, and technology) is valuable.

The point is though that future study doesn’t necessarily have a higher value than current study. Especially if the art is likely to degrade over time in some respects anyway.

>A copy of the painting can serve for viewing nearly as well as the original.

Maybe for a lay-viewer. As an amateur realist painter, even the very best prints seem to lose 75-80% of the mark-making and process clues that are easily observable in originals.

> A painting stored away in a climate controlled vault where no one can look at it is just a dusty canvas rectangle.

It may just as well not exist at all.