I see people on YouTube hammering/pressing in frets w/ out gluing them and then I think about “fret sprout” and that wood doesn’t just shrink in one dimension 
(and before someone mentions it, yes, I bet it does shrink more in one direction than another because of the grain/wood type/voodoo/the moon on the night the mother of the luthier that installed them had their child/etc)
Would be a bummer if the frets actually fell out 
just put in some wood filler, partial fretless!
find your signature tone 
Edit But yeah, if I ever end up fretting a neck, they are getting glued in. It costs practically nothing
It has happened, under extreme conditions, e.g., very prolonged high-heat/low humidity storage conditions can cause the fretboard to be desiccated beyond simple repair. Of course, in such an extreme situation, other issues are pretty much inevitable. This would constitute downright musical instrument negligence and abuse.
Well the plek machine isn’t going to do anything without a person telling it to which is why they require skilled operators to make decisions about how to best correct an issue.