Sure, but even if the paintings are a reference to Warren, it's hardly the one and only example of foreshadowing in the Buffyverse and I don't really see what it has to do with the current storyline. And also, if we assume that the Spike story takes place weeks later, it's nothing to do with determinism either; Willow had already murdered Warren by then.

The current storyline, however, is obviously going to play around with those questions a lot - is this what Willow will become or what she may become, is Fray's world the future or a future? I keep thinking back to the Doctor Who mini-episode Time Crash, in which the Doctor gets duplicated and his older self knows how to save the universe because he remembers being his younger self watching his older self saving the universe, even though it hadn't happened until he actually did it. Timey-wimey, wibbly-wobbly...