they are also chasing Orochimaru of the Sannin. He has committed some crime against the western alliance, and now everyone sends their hunters to search for him, reaching even here.
"there are/were hunters in Marsh, asking after Orochimaru" seems like the kind of local info Syoma is likely to be accurate about.
If so, that's.... really interesting. Oro sees Pain as an existential threat, so he's not just giving up on the rift and living the quiet life. I see two main possibilities for what could have happened.
Possibility 1: Akatsuki got pushy.
After Hazou's disappearanc, Akatsuki suspect Leaf is trying to pull something, and decide they want to check Orochimaru's work also. They're hesitant to forcibly breach The Basement, but Itachi tells Naruto "order Oro to give my SC full access, or we carpet-bomb leaf". Naruto relays this to Orochimaru, who decides to bug out rather than roll over(possibly on secret order from Naruto, possibly on his own).
Orochimaru is now in the same position as Hazou: missing, preparing to either Return To Leaf or Yoink.
Possibility 2: Oro!yoink
Orochimaru did the same maths we did, built a runic weapon, noticed he's an S-ranker with >4000cp (enough chakra to summon Manda and still fight on his own), stole the rift for himself, and went missing.
He's working on some mix of rune research and afterlife exploitation, and either constantly relocating or preparing a doom fortress. He may or may not have permakilled Hidan when attacking the rift.
If it's possibility 1, that changes fairly little for Hazou, other than making it Orochimaru who could pull the trigger on a rift assault, rather than Naruto(who currently has no way to manipulate the rift).
If it's possibility 2, that changes ~everything.
Instead of sacrificing every other consideration at the altar of research deadlines, we can step back and chill out a bit.
We have to stay missing, but short/medium term, we can research combat seals, raise combat stats, learn minatosealing, do scroll hunts, follow other plot threads, spam unstagnation adventures, etc. generally ramp up, adventure, and roam around like mini-sanin while we focus on coming into the fullness of our power. Very fun!
Longer term.... Orochimaru is a huge hecking problem, and is now the presumptive final boss of MfD.