What's the exact defect or injury we are talking about here?  A
free-floating sphenoid bone?

Anyway, in the absence of mechanical stress (blows or other rapid
accelerations), it may not matter, just as fractures in some other bones
and parts of the body may not even be obvious unless mechanical stress
is applied, because their natural tendency is to remain in the correct
position, anyway.

I suppose there are portions of the skull that might tend to come apart
if fractured, although nothing springs to mind.  A bone that is not
firmly attached to its neighboring skeletal structure in the usual way
but is nevertheless maintained in its place by soft tissue and/or
natural forces (no gravity or other stress pushing it out of place)
would not necessarily be the kiss of death.  So cracking the skull in
two halves would be dangerous because mechanical forces would tend to
open the skull, but removing a small square for surgery and then
replacing it isn't necessarily a problem as long as nothing applies
stress directly to the separated section until it heals again.