Well this is the drawback of SS design choice- combat and campaign are so separate, and there is a highly artificial, gamey border between them that can be bridged with an accidental click. (Not that I expect such a fundamental thing to be changed at this point, though it is sort of the Achilles heel of the game)
What if it auto-saved each time you took off from a planet? I often forget to save as well.
What you're asking for now means more "are you sure?" dialogs and boxes. Taken to its extreme maybe you'd be happiest with constant quick-save and quick-loading, which is a loathsome mechanic.
This has never happened to me, but if it really is a scourge for so many people, I guess if the confirmation dialog has a "don't show this again" checkbox it would be tolerable. It still seems unnecessary somehow.