In regards to Corella, he was definitely "frozen out" of the schedule last year. My understanding is that in the 2009 MET season, Corella was overcommitted (I remember reading about him flying to NY for an ABT performance only to hop on a plane to perform with his company the next night). Then in the 2010 MET season, he tried to cut down his commitments with his company so he could be in NYC for ABT, but McKenzie did not put him in the schedule. As for this season, Corella's company has been doing a lot of big tours and performances to up their presence (they are currently in WA state). I suspect that Corella may have put his company first his year as tour planning is done at least a year in advance, and he's made himself available for the MET season the best he could (at least Corella Ballet was in NYC in the fall). That being said, I hope that starting next season, ABT and Corella work out a better balance especially since as many others have mentioned, he's needed in the rotation.
Back to Stiefel, I definitely think that ABT is maintaining a relationship with him b/c of Gillian. That being said, I can't think of a dancer who's been flakier, for various reasons for difference commitments, in the past 5 years than Stiefel (injuries I can understand, although Ethan seems to be much more prone to them than others - perhaps due to how little time he has to actually spend dancing/rehearsing). His new relationship with New Zealand certainly complicates things as Gillian is slated to be a guest artist quite a bit, AND it seems like Ethan has managed to throw a wrench into the picture too...I know we shouldn't be focusing on dancers' personal lives on this board, but seeing as they sometimes affect their professional live...he did (finally) propose to Gillian on Monday night at the Gala (link here)...which means that it appears as though Gillian and Ethan will really have to treated as "one unit" now. I'm intrigued to see how long Ethan commits to New Zealand and what Gillian chooses to do. Losing either principal on a more permanent basis will be detrimental for ABT, especially Gillian, and I'd hate to see it come to that.