I don't believe there is any question it is just a matter of time. I was traveling to Lexington often when the smoking ban was being proposed there. Everyone was thinking "How can a smoking ban ever be passed in the heart of tobacco country?". Within a year, smoking ban is in effect in Lexington, KY. That was July 1, 2003. So in less than 16 years, there are smoking bans (to some degree or another) enacted in the majority of the USA. With the momentum shifted way over to the side of the anti smoking nazis, the matter of time you speak of is likely well less than 16 years.
My cellar just surpassed the 250 lb mark. By the end of the calendar year, I expect to be well over 300. If we're still able to purchase pipe tobacco from internet stores, at a reasonable price, 20 years from now, I'll be ecstatic about that. To me, that would be indicative that something happened that halted the highway robbery of our basic freedoms. It's been my experience, however, that one is best served hoping for the best but planning for the worst. While I'm not one of those survivalist Armageddon types in the least, having some gold coins, firearms and a robust supply of ammo stored with your tobacco would possibly be considered wise as well.