The guy you were replying to only made the longevity claim for Steam, not GOG. For GOG he pointed out that you can download the games DRM-free, so if GOG goes away, you still have the game. Anyway, for Steam I can buy the argument, it's the most likely platform to still be around, say, 30 years from now. But for GOG I'm not sure why you would think that. It's been in the news for supposed "financial troubles" just recently, and it's based in a country that does not have a particularly long history of political/financial stability. I actually see Epic having a more promising future than GOG, after all it's backed by a company with 10X the revenue and who also make the most popular game engine out there. And the aggressive tactics they're using right now show you that they're in it for the very long haul.