Unless it's going to be kept in the damp, it shouldn't decompose, it should just dry out and become brittle and even then the core of the stick shoudl last - after all, how long does dried, uncured untreated wood last indoors? Quite a while. The biggest issue is that bark will flake off as the twigs dry, but if the sticks were firm and the bark wasn't loose when you grabbed the stick, even this won't be a problem for years and years. It really depends on the condition of the sticks when you found them. For the helmet part, the bark has already separated, so I would be worried most about that flaking to bits.