tl;dr, proper solo career for Riho or bust.
This. Riho doesn't strike me as the type of person to ~do things for charity~ or other similar tie-ins; that made Mizuki and Teddy (Sakura) much more fitting for the Precure tie-in song earlier this year. I don't think she'll be looking for a major TV appearance afterwards as an idol. She seems more like the type to go the Risa and Reina routes, who found careers that they enjoy (plays and bands).
I don't think Riho will be gone from showbiz at all. She's been doing this her whole life and she's not the type of person to say, screw it, and give up to live a normal life. She's not Eri.
From Sohee at Jplop.
"Well, what I can say is... That since this year I've been thinking about my future. And I've been thinking about that I want to improve my dancing... And that made me realize I have to go "outside" and learn more. I was thinking about it a lot... and talked about it with the people from the agency too. (Sanma: Didn't they ask you to stay in the group a bit longer?) Yes, they did.
While I was thinking and bothered about it, I would be working as Morning Musume right and I didn't want it to become obvious that I was troubled by something, either."
"I want to learn about a lot of things I don't know right now. I want to watch many musicals and all and take in everything as much as I can. My parents told me to calm down a bit but I was very determined so I managed to get their approval, too."
Musicals? You don't learn dance from musicals. At least, not the ones from Broadway or Gekidan Shiki or the stuff that Risa's doing. I know jack shit about the theater circuit, but that's about as "formation dance-y" as they get. I was thinking more along the lines of modern jazz fusion performance/dance that we get here in San Francisco. And that doesn't make it to the top of the Arts page in the newspaper.
But, kudos to her for willing to go outside of the box.
I'm sure we're going to get a single. There's still two months left of the year and the last one was a bit ago.
I dunno. There's not much incentive for Up-Front to create a marketing project for a graduating member whose last performing day is in 60 days, especially when they have to weigh in items like outfits, music videos, publicity schedules, and the handshake and release events when she won't be in half of them at least. The current promotion run for Oh my Wish/Sukatto/Etc doesn't end until 11/29. She's got her week of OMGWTFBBQ spotlight in the news; I don't think that she'd like to extend her goodbyes as long as Sayu did, with the bus tours and the FC events and all that good stuff.
If all that sounds really bitter and cynical, my apologies; it's a lot of RL eating away at my personality and bleeding into fandom. Riho is my favorite in 9th gen and despite this year's showcasing of 12th gen and Eripon's acrobat skills and the cross-groups mingling, I feel like she would still have an important role in H!P. (Plus, what happens to the Lilium sequel?)
If anything, her graduation treatment is going to be a huge different from the last 5 we had (Aika excepting), And like others have said, she probably realized that she wanted to do things different from what management was trying to do, and decided to end things on amicable terms without having a row over it.*
*quoting Prince Philip here, sorry.