"Your Story" contains no details on the subject. "Our World" mentions several forms of lycanthropy presented in the series but I don't remember it ever mentioning the issue of unconsciousness. From the game's standpoint there is no "official ruling". Some options supported by the series and books are presented below.
Were-Creatures Remain in Their Last Form While Unconscious
Courtesy of Houdini, in Fool Moon the Alphas are knocked out with a drug while in their wolf forms, and stay in those wolf forms until they wake and consciously change back.
Were-Creatures Revert to Their Natural State Based on a Predetermined "Spell Length"
Dresden suggests in the series, and Billy references it in the RPG1, that the Alphas and other Paranetters are just channeling magic through a different paradigm. Shapeshifting is actually one of the things that Thaumaturgy can do in this system2, though Fred Hicks explicitly recommends using Beast Shape or True Shapeshifting to represent mages who use it for that purpose regularly.
Thaumaturgy's duration ends at sunrise by default3. However more or less complexity could translate to longer or shorter durations based on the time chart4. You could select a set length of time that the "spell" lasts with early cancellation being an intentional act on the part of the shifter.
Use Invokes5 and Compels6 on the High Concept to Determine What Happens
This is the sort of thing that Aspects are perfect for. You can always find an explanation to justify it, especially if you assume that the duration above is variable, but if the player is looking for an advantage by reverting or not reverting while unconscious ask them to pay the Invoke on their High Concept. If you specifically want to disadvantage them by doing one or the other, offer them a Compel to have that happen (which, of course, they can pay off if they prefer). If it doesn't seem like an advantage or disadvantage for anyone, then it really shouldn't matter which state they wake up in7. They can always shift immediately.
- 1 YS084, Take It From a Werewolf sidebar
- 2 YS282, Transformation and Disruption and YS283 margin notes
- 3 YS266, 3rd paragraph from the top
- 4 YS315, Time Increments sidebar
- 5 YS099, Invoking for Effect
- 6 YS100, Compelling Aspects
- 7 YS104, What's a Weak Compel?