I think what
@FrogReaver is going after are things like dream sequences, where play rolls on as usual for a while until the PCs wake up in the morning and realize everything they just did was a dream. They didn't use those charges in their wands, they didn't take all that hit-point damage, they didn't die (but might wake up screaming if they dreamed they did!) - that sort of thing.
Here the retcon, of course, is that none of it happened; and the question is whether this violates player agency.
I've run scenes and even one or two entire adventures like this a few times, usually without lasting consequence to the PCs other than a) they remember anything they learned in the dream as it was so vivid, and b) they keep any experience points they earned in it as experience is largely built on memory.