Thanks for your concern. However, you added nothing more to solve the problem.
Concerning the natives' matter, I put references of native grammarians as well as websites. All support using "will".
Do those who support using "be going to" have any point or reference for their claim?
Is it OK to see "studying hard / not studying hard" as a "present reality" as Swan calls it?
Yet, we have another problem: S
Some say that "will" is the right option that no one "intends or decides" to fail by not studying.
That's why I'm asking our native teachers' opinion here in this forum.
I hope they can help me settle it down.
Anyway, thanks again, brother.