There is fairly general agreement that Ahasuerus is supposed to
be the historical Xerxes, but there is no independent evidence for a
Jewish Queen of Persia Esther, for Mordecai, or the other figures in the
story - which of course doesn't prove they didn't. OTOH, the fact that
the names Esther & Mordecai are close to those of the Babylonian deities
Ishtar & Marduk raises some eyebrows.
D.J. Clines' _New Century Bible Commentary_ on Ezra, Nehemiah, &
Esther sets out arguments for & against historicity. He says (p.256):
"The current consensus of opinion on the question of the Esther
narrative is that it is a `historical novel' ... by which is meant an
essentially fictional story with probably a foundation in some
historical event." I am no expert on the Persian period but this seems
reasonable to me. I would add that as Christians we are to see it as an
inspired & theologically authoritative historical novel.
In line with my original post, I would urge caution about one of
the arguments sometimes cited against hsitoricity, the rather improbable
coincidences which are crucial for the plot. That is sometimes what
makes genuinely historic eevents historic & not just historical. The
battles of Gettysburg or Midway furnish examples. & the implicit point
of Esther is that those crucial coincidences are providential.