The FBI Director has a ten-year term, indicating his job is not permanent (see J. Edgar Hoover).
Director is not automatically replaced with a new administration, but still serves at the pleasure of the president. Director can be dismissed for ‘cause’, but ‘cause’ is undefined and broad.
See William Sessions and Bill Clinton.
In that case, Trump needs to unload Comey. Or, perhaps Trump has some particular reason to keep him around for a bit. i hope it’s one or the other and not that DJT just hasn’t got around to it.