Chances Gog will actually sell it?.
The only reason they used DRM at all on the Runic version of Torchlight was to make it so you could easily activate your demo copy and keep playing (they've constantly refunded activations throughout the life of the product) and they made good by releasing a 100% DRM Free boxed copy like 2 months later, I think these guys might be willing to do a GOG deal (since we tend to simply download the whole game here, instead of download demo, play, buy and activate). On launch, 2 months later? Dunno. Are GOG and Runic even talking? Again, dunno, afaik Runic has been completely mum on what other digital retailers would be selling TL2.
Well I remember reading somewhere on their forums from one of the developers that no GOG on launch, but it seems it will be here a few month after launch. I think for now all pre-orders are either steam (multiple DD sell the steam version) or PW and at launch it should be available to buy directly from runic.