Agree with abatt. The Donizetti has a Bournonville quality to it - intricate, clean dancing, everyone having a good time.
Today I thought Whelan was even better than last night (or I watched her more closely). She seemed more ethereal. An "old-timer" told me at intermission that Allegra Kent carried off the poet's body from the center of the stage - a long ways! I saw two things go flying - one was the shoe, directly toward the Coquette in the downstage right corner, and not sure what the other was.
Why should Firebird be retired? It has great music, great dancing for the firebird, nice dancing for a lot of other people, beautiful sets and costumes, children love it (so do I), and it occupies a special place in the history of NYCB.