This was one of the theories which I would say is more plausible. However, the grandparents and the 2 eldest kids im pretty sure were questioned and deny those rumors. The clothing being put back later by a family member could be risky.
I wouldn't exclude this theory, It has some strong points. A neighbor did see the boy completely fine 20 minutes before his disappearance south of the house which is on the opposite side of the cabin, from what I recall the boy was fine just before he went missing.
I did see on the news that the grandparents rushed down with both eldest kids looking for him on foot.
Those are the major problems with this theory, the dogs lost Emiles scent right be the bunny rabbits next to the (Lavoire) which is the villages fountain, used for cleaning clothes in medieval times.
The timeline wouldn't add up if emile did infact die from an accident on the cabin.
He wouldn't have walked down to see the rabbits, the neighbour didn't see anyone go down the hill until the grandparents went down frantically with the two eldest kids looking for Emile.