How would one undo loading a quicksave in Kerbal Space Program?

I know this is an old post but it IS possible to "undo" a quickload because I've done it before more than once with 0.20 and 0.22.

The key is to react as soon as you realize what you've done. In Windows, just hit Alt-Ctrl-Del and bring up the task manager, select ksp.exe from the processes tab and click on "End Task", this will kill the game. Restart the game and load your mission, then you will be at the point where your game last autosaved, before you did the quickload.

This works only if you do it quick enough, because a short time after the quickload mistake, the game WILL autosave again which will overwrite the persistent file, but it doesn't do it right away, and a quickload does NOT overwrite the persistent save file.

Again, I have done this more than once because I've made the same mistake, and I can tell you that it works.

For anyone who does this now, I found a 'Backups' folder under the saves directory, which appears to have copies of persistent.sfs made at the last autosave - they could be useful - and saved me a few hours. YMMV.

As with saves in most games featuring a save system, no extra data is saved while loading. This means that, whenever you load (be it quick load or otherwise), your game reverts to the state it was during the save you're loading. Once you've gone back, there's no way to load into the "future" again unless you have a later save (which includes autosaves - they linger if you force-close the game soon enough after quickloading) in store.

So, in summary, there is no way to load forward to where you in this case were. The progress between your latest save (which, as mentioned, includes autosaves) and the point you loaded from is irreparably lost.