Some years ago I put up several batches of tobacco in vaccum-sealed bags, and eventually smoked all except one which somehow got pushed to the back of the cabinet and I overlooked it. Later I rediscovered it and decided it would be a good candidate to test long-term tobacco storage in vaccum sealed bags. So I put it back and decided to wait.
I did this because although I asked in different online forums about it, I got only replies such as, "I don't think it will work because..." or "it might not work because..." or "sounds like a good idea! let me know how it goes..." No one ever gave me an unequivocal yea or nay on the subject.
So let me now tell you, after 4 years and 3 months of storage: It does not work. So if you're thinking about this method for long-term storage, forget it. You will only waste your tobacco.
The tobacco in question was 2 ounces of C&D's Bayou Morning. Upon slitting open the bag, the tobacco had hardened into a near rock-like chunk. Small pieces could be chipped off which immediately fell apart into a nearly dust-like powder.
And that's that.