Can you link to where he talked about Yamato coming back? I haven't seen that.
https://onepiece.fandom.com/wiki/SBS_Volume_113
It was talked about in SBS 113.
Firstly, Oda lists all the official positions of all the scabbards. He lists what daimyo of each region they are and listed Nekomamushi as the “Leader of the Yakuza” and Kin’emon as “Great Elder”, the leader behind the scenes. However, for Yamato he simply says “she’s still learning about the world”. Not giving her an official title in Momonosuke’s court. She isn’t his “teacher” or “guardian diety” as others who didn’t want her to join said her role would be. She isn’t even listed as one of the scabbards. Which makes sense, as I’ve always said, Momonosuke sees her much like Luffy. An outsider who isn’t responsible for Wano and it’s day to day goings on and upkeep.
The second mention is in regards to a reader saying something in regards to “Someone told me that characters that appear in cover stories will no longer appear in the main story. Is this true Oda?” This was right after Yamato’s cover story had just come to an end so this person was assuming that she wouldn’t ever appear in the story again.
Oda explains that cover stories are basically meant to explain what a character has been up to before reappearing in the main story and that you should “look forward to whenever she appears again”. Essentially saying that her story isn’t over yet and don’t write her off just because appeared in a cover story.