The piston on my Avid Elixir 5 brakes popped out. Does the caliper need to be rebuilt?
sram has always been awesome about providing excellent manuals for their products.

http://cdn.sram.com/cdn/farfuture/5Pyt9L0OIUi7XDfIWNl65p9qoT3H9ULX2vOahNqzavo/mtime:1330363328/sites/default/files/techdocs/elixir_5_service_manual_rev_b.pdf

I would recommend a quick rebuild to make sure the seal for the caliper isn't damaged. See page #19 of the above PDF. 

Should be easy, just be ready to bleed your brakes ... ( a pain with elixers ... sorry!)