Devil's Child Nico Robin stood at the precipice's of distinction. Had she died during the Water Seven saga, the manga would've improved drastically as each character now knows the sting of loss and defeat once more. Not to discredit those backstories where childhood tragedies exist already, but for the entirety of the crew to strive to rescue their endangered and estranged ally, only for the clutches of the government to drive forward & extinguish Nico Robin's flames, would have only benefited One Piece. The maturity thrust onto the story & the changes to stem from it would provide the direly needed development for our favorite pirates.
Atonement for Alabasta and her participation in Baroque Works is still required from Nico Robin, this early exit from the series cements the fact that prior consequences do haunt you. Perhaps, foreshadowing for later in the series?