I think it's an open end which is up to the audience to decide, at least I'd like to think of it that way.

The thing is with the stakes of their dares way up high, if Julien and Sophie survives at that point, they'd still play their game, which is their way to express their love to each other, and live happily ever after. If not, they die together loving each other..

One way or the other, they still love each other, their love will last forever against all odds.