Well, I have heard many singers since, some greater musicians than Ivan Rebroff - but as someone possessing a pure vocal gift, with direct appeal to the emotions - probably none better. To be able to sing from darkest deep bass to sweet falsetto soprano... well that would suit me just fine.
A singer such as Rebroff would - I feel sure - make a good living and bring great pleasure among any people, in any society, at any time in history.