Originally Skulduggery Pleasant (Book One in the series) was twice as long as the published version, it had Baron Vengeous, Sanguine and Scapegrace playing important roles, plus a whole plot where Valkyrie Cain invisions her future.
In this original version, the Reflection did not feature and as such Valkyrie was frequently getting into trouble at home. Derek decided that he wanted Valkyrie's home to be a refuge from all that went on in her professional life as Skulduggery's companion, so created the reflection to make her home life as pleasant as possible.
What Might Have Been is therefore a collection of scenes that involved Valkyrie's personal life and her getting into trouble with her parents and the people of Haggard. They were featured at the end of the Australian version of Dark Days and at the end of the non-Australian, World Book Day novelette entitled The End of the World.
Altogether there are three What Might Have Been Stories, called Part 1, 2 and 3 respectively. Part 1 originally stood right before Skulduggery and Valkyrie broke into The Vault and a remnant of this scene still remains in the original book. In said scene, Stephanie is returning home from staking out the Vault and is qustioned by her mother , Fergus and Beryl about why she was in Skulduggery Pleasant's car. She lies about their activities and Beryl insists that she has fallen in with the wrong crowd. Eventually they give up and Valkyrie's mother sends her to her room.
Part 2 occurs after Valkyrie was poisoned and as such has been unconscious for 26 hours. This scene is essentially her telling her parents that she is alright, having gone missing for the past 2 days. Valkyrie lies and tells them that she went to Gordon's house and fell asleep. Her mother is extremely angry with her and so is her father . It is left wiith them questioning what changed in Valkyrie's life to turn her into this daughter and they eventually reach the conclusion that the inheritance has changed her.
Part 3 is part of the original epilogue and is a summary of the events in the book and shows how to people of Haggard think that Valkyrie is a deliquent who has fallen in with the wrong crowd. Interestingly enough, it also states how Tanith Low was killed by the White Cleaver instead of injured. Derek also talks about how Valkyrie's mother hadn't spoken to her in weeks and how her father could not look her in the eye. Also, in Part 3 it is shown that Gordon had, unintentionally, written a loophole into his will meaning that Valkyrie could only inherit the money and estate if she was living with her parents. It also transpires that Fergus and Beryl had been trying to create a rift between her and her parents so that the inhertience went to them. Finally, it is shown that Meritorious is still alive and is holding together a rather shaky Council of Elders.
Derek ends with a small anecdote about his cat and ends the novelette there.
Since these scenes were replaced, they are deemed non-canon in the Skulduggery Universe, the first (and only) time a non-canon source was published.