If I was to make an easy answer, it would be that Harold Ashby took over Jimmy Hamilton's tenor role, and nobody took over Hamilton's clarinet role, although Norris Turney added a flute voice.
But Duke...when you start thinking strictly in terms of "instrumentation", that's already drifting over into Missing The Whole Point Land, I think. Sound uber alles in Ellingtonworld, the more I hear it, the more I hear that....voices, colors, not "instruments"..in that regard, I think "we" might have already praised Duke in excess of our still-evolving understanding of him. that stuff keeps revealing and deepening as time goes by, the less of it there is in the "real world", the even more distinctive and unique it becomes, and as conventional perceptions become irrelevant, new findings come out....you (ok, "you") can listen to this stuff forever (ok, "forever" and keep hearing new angles, perceptions, colors, interior, exterior, micro, macro, the world of Duke Ellington, indeed.