IIRC, the fix for this is to mix quite a bit of matching wood sawdust (ebony in this case) with a suitable super glue, make a black paste, and fill in the crack neatly. Then sand smooth. Will take more work here with the fret and inlay involved, but certainly 'do-able' by the right guy. But that should make it plenty stable and stop that crack in its' tracks.
See kids, OIL that fingerboard ! ! !
If everything is legit here, that's a deal.
J o e y