I'm curious that, should the Ryuki or Knight get a re-release, would they include their Contract Monster?

Almost certainly. Both have accessories that are directly connected to the Contract Monster, especially Knight and all of his cape options.

I'm wondering about possible future Ryuki figuarts, like Odin, Femme etc. Will they get their contract monsters included or will they be exclusives like Genocider or will they just get cut entirely?

Femme I could see coming with hers, since she is basically a female version of Knight. Odin...I doubt it. It never really even showed up in the show.

But they could easily cut prices by just including their various weapons and accessories.
Like, rather than including the entirely of Dragredder, they'd just have the tail for Sword Vent and his arms/legs and torso plates for Guard Vent (If I recall correctly, the Strike Vent head wasn't actually a part of Dragredder).
I don't own a Knight, so I'm not sure how much Darkwing contributes to him.

Darkwing is pretty indispensable. His upper body forms the clasp for all of his cape options (one of which is his wings and lower body). If they cut Darkwing out it would just be Knight with his Darkvisor and Sword Vent.

If Knight gets re-released, it'll be exactly the same packaging and mould. Things would only get changed if they released a "new version" like Crystal Skull or Violent Emotion Decade.

I think the rest of the riders themselves will probably be exclusives, except maybe Odin. The rest were pretty much one shot villains who didn't last long, similar to Gai. I don't think we'll see anymore of them packaged with the contract monsters either, that was clearly just a way to one up the Figma's.

Or if they were correcting an error, like the bow legs Kabuto figures.

Well, I started putting my Figuarts back in their boxes today to get ready for moving Thanksgiving weekend. I think Shadow Moon cried a little.

Of course, there is no way in hell I am going to even attempt putting Dragredder back into the box, so I'll just have to be real careful with him.

It's not getting him back in the box that's the problem. It's trying to ever get him back into the same pose you had him in the first time :lol