I personally do have pre 1.1 installer backups for KSP downloaded before the update, but that is wholly beside the point. The issue at hand here is one of reality matching rhetoric. Galaxy users have access to functionality that non Galaxy users do not, despite this being readly achievable without the need of a separate client in order to do so.
I see your point here and like i said above, it would be nice for the non-Galaxy users to be able to downgrade, but don't forget that it's not GOG's fault that KSP is not stable for some people (or some people don't like the newer version for some reason), the blame is on Squad*. Galaxy it IS** optional - you can install, play & update the game you bought without using Galaxy.
* of course, i don't actually blame them for anything - in fact i'm glad they continue to support & upgrade the game we all love to play and such complex game can't be devoid of bugs, especially during the whole transition to Unity 5 phase.
**so far and i would like to believe that this won't change in the future.
This makes the statement that Galaxy is and will always be "totally
optional" an extremely dubious assertion. Whether by design or by ineptitude, this is no longer a claim that GOG can make in good faith.
The same could be said about achievements; Galaxy users have achievements and what else but those who don't use Galaxy, don't have them. That doesn't make any difference on the "optional"
part for me, even though non-Galaxy users have sort of reduced functionality.
Having said all that, i would like to believe that if someone really has a problem with the current version of KSP, support would be able to fix it for them by actually providing them a link to a previous version of the game. Anyway, time to have fun with 1.1.2 - i hope there won't be any critical bugs this time! :)