Little Busters Kudryavka Route Ending explained

Naoki-Saten: I only just figured out the whole meaning of the Kud route finale. Wonder why the heck it took me so long. >_<
If you didn't already figure it out, then I'm afraid I'll be sending you more brain pain now ^^
That deus ex machina is not a deus ex machina at all. In fact, it's more of a metaphor!

We know that Kud regretted not going back to her mother in the real world, therefore her route 'punishes' her by executing her mother if she ever chooses to not go again. On the other hand, it enables her to revise her choise and clear herself from regrets.
HOWEVER: There are still more regrets beyond that. What Kud regretted most is not being able to become a cosmonaut, or generally, not being able to become as great as her mother. That's what she was talking about when she was chained in that cave and that's what the dog tag/machine parts represents. Well, the CHAINS that are physically binding her in that cave represent the very same thing. Those are the chains that mentally burden her. Because she thinks she is a 'useless gear'.
So by throwing away those machine parts, she overcomes her regrets, thus shattering the chains binding her. In the end, it was all a metaphor.
No deus ex machina there. It's all the work of Kud with Riki's help.

Of course, you have to know about the imaginary world and it's properties to figure that out.

Nice. I actually re-played the finale of kud route to verify my theory. Even found another hint to the secret of the world ^^

(another message later)
Well, regrets about not going back to her home country are part of it, too. In fact, they were the bigger part of it. She was supposed to go back but she stayed in order to be close to Riki. She thought that was a selfish thing to do. Thus, she remained a 'useless gear', and maybe dying as a sacrifice could fulfill SOME kind of purpose for society.
But Riki helps her overcome that guilt.
"Don't you want to come back? Reach out for my hand, Kud! If you love me... if you truly love me then reach out for my hand!"
After all, regretting not having come back to Tewua means regretting to have stayed by Riki's side. And there's no way in hell Kuu-chan would be able to regret that, right? ^^
Thus, making Kud realize her true feelings, Riki helped her shatter those chains.