As others have pointed out, "high-stakes" isn't just sort of right, it is precisely correct. The variations "all in" and "all or nothing" don't tell us enough about the success condition (high payoff is merely implied), only that failure means losing everything. Unfortunately, the most frequent occurrence of "high-stakes" is from unimaginative journalists and reality TV narrators who love to say things like
"... in a high-stakes game of [some spectacular-sounding activity]."
where the activity would never have sounded spectacular without the dramatic color added by the phrase "high-stakes". Sort of sad, isn't it?
That particular term is now crippled. To an audience it flags a situation as canned or the narration as overblown, and is more likely to decrease their sense that the situation is of genuine importance.
I would recommend a term like "gambit" or coming up with your own turn of phrase that says precisely what you mean without resorting to tired literary/narrative hacks. Its OK if the audience pauses for a moment to consider what you are saying -- that indicates they are actually digesting your phrase instead of blowing past it, assuming they know what you mean.
Making something up based on your "cave that you fear" example:
As you approach the cave pinpricks of excitement mix with temors of dread. You realize that entering will bring your exultation or your doom.
Or something along those lines. Thinking in the context of a game where you might have a voice actor, a book where its the reader's inner voice, or some other situation like a movie where the events are external would heavily influence the exact words I might use.