Hi,
I must say I don't know much about it's general stability in air but I don't think anything bad should happen to it. It's not very hygroscopic - according to 'wikipedia' it takes almost 2 months for it to absorb 0.03% of water in 80% (standard?) humidity. Another forum, however, claims that it absorbs moisture quite easily. If it's not lumpy, sticky then I think it should be fine... You could do a small test - take a portion, weight it accurately [perhaps grind it] and either dry it in vacuum dessicator or in the oven at 120-150°C? See if the weight changes a lot and if it turns nice and crispy. It melts at 334°C and decomposes above 400°C.