Which piece is least likely to be taken? If one were to analyse a large number of chess games, which specific piece (not type of piece) would be found to be taken the least number of times? And yes, in light of SomePatzer's comment, besides the kings of course.
I recently looked into that very thing a couple of weeks ago, and found an excellent breakdown on it (just this one, though):

The short answer is that aside from Kings, h2 &amp; h7 are the least likely to be captured pieces (with survival rates claimed to be 73.92% and 72.29%, respectively).

Regarding individual pieces' survival (from a 2,196,968 game database), http://www.quora.com/What-are-the-chances-of-survival-of-individual-chess-pieces-in-average-games/answer/Oliver-Brennan gives a table (and an accompanying graphic) of each piece's respective chance of survival.



While I was at it, I found some data on square usage. I've included the sources below not because square usage relates to your question directly, but because the nature of the two topics is so close that I figured that they might be of interest to you (or future readers).

Using 509 games selected randomly [and analyzed] out of a 567,000 game database, these two URLs give tables of raw events and normalized through-traffic usage of squares, and heat maps of same:


http://sarcasticresonance.wordpress.com/2010/10/05/chess-territorial-2
http://sarcasticresonance.wordpress.com/2010/10/13/random-chess-conquests/


This URL analyzes the moves of 12 Grandmasters' entire careers (separated by white and black, all normalized [no raw counts]), along with some graphs of average-data counts:


http://en.chessbase.com/post/seth-kadish-visualizing-chess
http://en.chessbase.com/post/study-of-square-utilization-and-occupancy


There are also some excellent analyses (per side) of each type-of-piece's square usage at http://philanalytics.blogspot.com/2014/11/chess-analytics-analyzing-championship.html .