I feel like it'd be easier to make a seal to selectively lock away memories than go missing Nin like that. Maybe the Yamaka have something? Grue ourselves basically.
We can't fail deceit rolls for secrets we don't know we have!
Hazou would have to have Medknow high enough to know how to interact with the exact portions of the brain that contain specific memories, and then he would have to have biosealing high enough to interact with the brain in such a way that it seals key memories away... and does nothing else.
Doing brain and memory stuff is hard as heck. Mari, who has made a huge amount of her own genjutsu, made Truth Lost in the Fog. By her own admission, it is her Magnum Opus. However, it also causes severe brain damage to her every time she uses it. So making a bioseal that locks memories away is going to be a Very Difficult Thing, never mind the viability of getting access to biosealing (and raising it that high) in a close enough time frame to be relevant.
...and then, unfortunately, you have to consider the actual research process. In both seals and bioseals, Word of God is that a sealmaster churns through several prototype seals before creating a final product.
With biosealing, that often means working on civilians and ninja --fellow human beings. I could see the research process of creating a memory bioseal leaving a lot of damaged people.
And, while Hazou's relationship with Leaf civilians is unbalanced/high enough that we would likely have no end of volunteers, desperate to "give back" to the Clan Lord who gave them and theirs so much... I wouldn't want to ask that of them.
Side note:
Speaking of civilians, have we considered what the reaction of Leaf's civilians will be if Hazou goes missing? We're all but worshipped by them due to all our Uplift Projects. If we leave Leaf, they're going to be very, very displeased with the people who made their hero go away.
Double so, once the new Goketsu Clan Head stops all of our insane Uplift Projects (such as funneling our own money into the Tower's Till'n'Fill Missions to make them actually viable to take and still pay rent).
Triply so, once they find out that we ditched Leaf because Naruto forbid us from trying to resurrect Akane (who was a first generation ninja, and widely beloved by Literally Everyone).
I could see Leaf's civilians (or at least the Goketsu's "many hundreds" of civilians) doing something in reaction to that. Refusing to work, slowdowns, malicious compliance, etc.
In Leaf, civilians (nominally) have rights, but it wasn't until Hazou came that they were treated like it. Mari, herself, said that Goketsu Civilians have a quality of life only found amongst civilian nobles. And Hazou's name is becoming echoed throughout Fire's hamlets. Hazou makes civilians
actually feel protected.
If he goes Missing, then... welp. I suppose it's the civilians' turn to unionize.
Edit: sorry if it's rambling. Still sick, despite water, naps, and medicine.
