I don´t believe that Richard is saying goodbye, just that MK is going to be out of touring this year, so he can tour with Neil without problems...
When he says "Scarcely retired" I guess he means that maybe he´s not recording that much as a session player, and that he´s only touring with MK, and there is no MK tour in the pipeline, the "co-operative scheduling" obviously means that he asked MK before just in case he has plans for this 2017 and avoid having to refuse touring with him because he is already touring with Neil Diamond...
To me, that means he wants to tour with MK again, and that probably he knows when MK wants to tour so he can arrange his schedule...
I don´t think that MK ever thought about replacing Richard for a long tour, they are friends and MK values Richard talent a lot, but probably for other kind of gigs, probably McIntosh would be his choice.