I would use it as is. You can't make the crack go away and, frankly, it's not going to get much worse unless you jam the razor in the scales again. It's been like that for decades and that's how it will end up staying without further stress. While ivory does not do all that well when pinned securely to solid materials like a fixed blade knife, with a razor, it's pinned only to itself. The problems with ivory usually come from being pinned to something that doesn't expand and contract the same way the ivory might.

As I noted earlier if you pay attention to ivory scaled razors you will find that in almost every case of cracked scales the following is true.

* It's the wedge end only
* It's only the scales on one side that crack.
* The crack rarely extends more than a few inches from the pin.

And that's because it's not cause by natural shrinkage and contraction, but by the force of the scales being wedged apart by the blade.