Yes, I do believe Yamato leaving is really a question of 'when', not 'if'. I'm strictly talking about at the end of the current Wano arc, which seems like it's probably going to be 1057 or 1058, Oda hasn't really developed Yamato's character in a way yet which is conducive to her leaving.
But I do agree with you that Momo could catalyze her departure in the future. He could even go with her.
This is a bit of an out there theory I've mentioned a few times, but Aramaki made clear that there is no line which cannot be crossed when it comes to non-member nations. Both Yamato and Momo humiliated him to some extent, even if Shanks is the one who scared him off.
I've wondered if perhaps his payback could be placing a bounty on the country's rightful sovereign.
But that's also built around my, perhaps incorrect thinking, that all those Luffy really considers 'nakama', his closest friends, will get to be present for the discovery of One Piece. Thinking that if the reason Luffy didn't say goodbye to Momo & Kin is because they're already considered 'nakama', that he would find some way to have them with him when he heads for Laugh Tale and I could see that extending to Yamato as well.
But again, that's really entirely speculation - and maybe Momo will just inspire Yamato to leave at some point. He did say he wants her to be able to leave.
I do have a hard time seeing Momo leave Wano by choice or by force after such a long time of buidling up to him taking over as Shogun, but times change and given enough chapters, who knows what will happen.
There was once a time when Vivi eventually returning was a very unpopular theory and look where we're at now.
So, it's absolutely possible that Yamato forging a close bond with Momo and Wano means staying now, leaving later.
And at risk of repeating myself from the previous post, I think that further character development would entail either handing over the reigns of 'being Oden' to Momo, as Yamato seemed willing to do in chapter 985 to Luffy, or it means some other change either on Wano or in the world, some other mission or discovery or... something which gives Yamato an Oden-inspired reason for not just sailing the seas, but specifically supporting Luffy's bid to become Pirate King.
Like, thinking back to the barrel scene in chapter 100:
"I'm going to become Pirate King!"
"I'm going to become the world's greatest swordsman!"
Right now, all Yamato has is "I'm going to leave because that's what Oden did!"
Maybe in the future, she wants her own adventure. "I want to really be free like Oden, which also means no longer trying to be Oden or following his exact path" Maybe she has her own dream beyond that.
But it could also be something like, "I want the world to be free like Oden" or "I want to know why the borders need to open."
Just, something to either chart her own course or to blaze a new trail past where Oden's journey ended, finding some way to build on his will or dream by accompanying Luffy.
There are a lot o possibilities.