Eric -

the thing that might concern me is being as the crack appears very narrow, the "repair" may require that the crack be opened up a bit to accept whatever material he is using. Personally, I think that would exacerbate the situation as far as the aesthetics are concerned. In other words, it will make it more noticeable. Rod suggested using some compressed air to get the dirt out. I imagine that would improve the appearance dramatically.

My guess is the crack could be relatively stable, like a small stress crack in concrete. It moves, but doesn't adversely affect the structural integrity in many cases. Like was previously mentioned, may not worth the effort unless it was to fall off which seems unlikely.

I don't recall seeing any major failures with ivory like the handle fell off, lost a piece, or chipped. I would say only perhaps from impact might that happen.