Paul Pierce with no titles easily gets his number retired.
If Rondo continues playing at this level his number gets retired. I feel his is still improving.
One thing to take into consideration is Max had his number retired.

Nice player, bad pre bird team he one of the best players. After Bird arrived he was an important cog in the machine and except the finals mvp just a cog. Looking at complete game and stats compare PP and Max. No comparison. Max is a sub on this team.
DJ, love him and I've said this many many times (finally happened) he belongs in the hall of fame but I can't see him having his number retired. Or at the least he deserved to be in the hall before his number was retired. Incredibly important part of the Bird era, great player who was better before celtic days. Anyone who got to see dj in seattle saw quite a basketball player (and team) Look at his celtic career, how many years, the stats, great defense. Compare young mr rondo's current career with dj. I feel if rondo plays 10 years with the c's he's a lock, at his current level. Again I think he will be improving more. Once the big 3 are gone, his triple double numbers will jump and he will dominate more because he will have to.
I feel the celtics do not retire a players number because of championships.