This might come out jumbled but just a thought after rereading a few fics. 

All of cannon happened. (All of it). With Joyce watching from the heavens above. She decides she hates how the Spuffy story goes and complains to the ptb. The powers realize that a lot of what happened in the world didn’t need to so they figure if they go back to a specific point in time things can change. Joyce points out willows will be done spell saying that if spike and Buffy stayed together a lot of the things that did go wrong wouldn’t. So when willow casts the spell reversal the ptb make it so our favorite couple realize they really are in love. Willow keeps trying to reverse the spell until whistler shows up and tells them all there is no spell on the power couple they actually are in love. From there the story could end or if you really want to make the world a better place they can continue through a happier cannon.