I think, with the way saves are stored, they can disappear if you cleared your cache? In any case, I don't think there's a way to get them back. But an update is coming soon (by the end of the month) so I would highly recommend replaying when it comes out since I've added/changed some bits as well as tweaked with some variables. (but if anyone doesn't feel like replaying, there's also an added quick-character creation to jump into chapter 5).
One of the other IF authors posted that Itch.io was changing how things work and that it would affect the saves of all IF games. Unfortunately, if you hadn't saved to disk your saves prior to this change, you'll probably have to replay everything again. From now on, make sure to save to disk as your saves won't be safe.