What happens to the shared library on the filesystem when I drop a NATIVE unit?
Up until 9.2.0, nothing. The shared library was not garbage collected. In version 10.1.0, when a natively compiled unit is either dropped or recompiled in interpreted mode, the shared library is deleted both from the ncomp_dll$ dictionary table as well as from the the file system location specified by the plsql_native_library_dir parameter. In case of RAC configuration, the shared library is deleted from each instance’s plsql_native_library_dir location.