Craig did say indeed that TSoG, like TPA2 will be a buy-only game.
From what I understand from his comments, at some point, relatively soon, he'll stop undpating the public demo, but I'll be very surprised if that is actually taken down- it probably wouldn't be simply updated, that's all.
Well, Zackirus, it's the same problem all the time, when you are trying to sell a product, in this case- a game, and you have unknown strangers testing it- some may not be very honest and may leak the game elsewhere, pose it as their own work (and try selling it), or simply give it online for free. I am sure Craig will keep it open for as long as possible, but there was this form of feedback from many people which Craig mentioned on the forums: that after playing 90% of the game for free, they didn't feel like buying the whole thing. So, the public demo will probably be open to the same degree as the official free TPA2 demo.
Incidnetally, im2smart4u, did you buy TPA2 in the end?