Isabelle, do you realize that this species is sometimes deciduous in nature if conditions become cool and dry enough? Although, in cultivation if is often not deciduous because the conditions we grow our plants in are too warm and wet. Putting the plant outside could've easily caused it to go into dormancy. They normally only have 1 to 2 leaves; it doesn't take much to cause the plant to abort a leaf or two and go into dormancy. If it was cool and dry enough, your plant's foliage might've dried and died; but, the roots and stem would remain alive and after a couple months, with the return of warmth and adequate moisture, the tiny bit of stem would begin making new foliage again and it would come back to life. This species is best mounted because the roots are highly photosynthetic. That's why they are so flat; they can catch the most light that way. This helps them to survive the periods of being without any foliage. I hope you still have your "dead" plant. Maybe it can be revived?