I get where you're coming from but a similar event happened with Mitsutoshi Shimabukuro (author of Toriko), where his big hit series, Seikimatsu Leader Den Takeshi!, was cancelled because of him violating CP prostitution laws. Even now Takeshi's brand was ruined because of the case, although Takeshi never had an anime unlike Kenshin. He was able to write an ending for the series in Super Jump magazine but that was after the scandal.
Takeshi was serialized an issue before One Piece was competing with OP, along with HxH, in fact all three series were the pillars of WSJ at the time. It was big but definitely no where near as big as Kenshin. Also, Watsuki's case is worse than Shima's case since at least from what I remember Shima was using a dating site and it's possible that he didn't know her age, plus she was 16 but Watsuki allegedly said he has preference for girls in late elementary school.
I noticed on twitter, japanese are bringing up the case of Shima so I don't really know how it'll go from here. My prediction is that the brand of Kenshin in general is "ruined", it will still be remembered as big a success since that can't be taken away but what I meant is that it won't be mentioned as much when people think of their fav./big shonen jump titles. You probably won't see much of it when it comes to Jump events either.
Edit: I wonder how Oda is taking this since Watsuki was his mentor. He may reconsider having homages to Kenshin in the Wano arc now.
