There are some dancers who will never make it out of the corps. And for some of them, that is OK, really. Being a soloist or a principal means many many extra hours of hard work, particularly if the dancers are lucky enough to have a new piece set on them. (i.e. choregraphed on them). Also, some dancers want to take time to have kids or to begin to pursue other educational opportunities.
Here in the Bay Area, many members of SF Ballet are able to go on and complete a college degree at ST. Mary's in Orinda, which works with the ballet to set up programs in which the dancers can participate. Some of them do exceptionally well post-ballet, such as Molly Smollen who went to St. Mary's, then got a law degree from the University of California's Boalt Hall School of Law (a very prestigious law school), and now works as a deputy district attorney. So they don't all necessarily go into dance-related occupations after their dance careers are over.
The speed with which as dancer leapfrogs from the corps to principal dancer status is variable, at least with SF Ballet. It depends on a dancer's talent and also on the needs of the company. SF Ballet this year has had a large number of promotions, possibly related to the retirement last year of three of the principal male dancers and this year to the departure of two female principals and one male. But the youngsters who got the promotions are simply dripping with talent. It's so exciting to watch them.
Dancers with most of the major U.S. ballet companies are members of a union, the AGMA, which also represents opera singers. Typically a contract is for multiple years, and will come up for renegotiation in the year before the end of the contract. Dancers always want more money and better health insurance and benefits, and the companies try to hold the line financially. It gets tricky and will get even trickier now that the guy in the White House has effectively gutted the National Endowment for the Arts, which supplements a lot of companies' budgets.
My season tickets are quite expensive. I think I end up paying almost $2000 for a pair of pretty good season tickets. It's a HUGE hit for me financially every year and means that I have to give up many other things I'd like to do. (But for me it's totally worth it to be able to see one of the greatest ballet companies all season long). And yet I know that the ticket prices don't go anywhere near paying the cost of getting the curtain up. Ballet companies -- and opera companies -- are very expensive luxuries for a community. Fortunately here in the San Francisco Bay Area, we have a very strong tradition of philanthropy, and the ballet and the opera's development people have begun to cultivate people with some of the new tech. And many of them seem to be willing to support the ballet and other cultural institutions. When I can, I toss a few dollars in the ballet's direction myself, but my contribution is very tiny compared to many other people's.
I think you asked about casting. Again, my present-day experience is pretty much limited to SF Ballet. For example, the company is performing ``Swan Lake'' in the next couple of weeks. I think there will be 13 performances and there are four separate couples who have been rehearsing those roles. Right now I can go to the company website and see who is dancing the lead roles on the night for which I have tickets. Some people who are fans of particular dancers will wait to buy their tickets until casting is announced, typically within a week or two of the performance.
With SF Ballet, a dancer may well be in the corps for one ballet, and then have a chance to perform a soloist or principal role in another, all in one season. SF Ballet really does give talented people in the lower ranks lots and lots of opportunity. But this is decidedly not the practice at Paris Opera Ballet, the Bolshoi or the Kirov, where ranks are rigidly maintained.
Speaking of ranks, here's a video you might find interesting. It's of the grand d?fil? of the Paris Opera Ballet on opening night. All the dancers, from the youngest of les petits rats of the school of Parish Opera Ballet to the most esteemed etoiles (stars) enter in ranks to the march from Berlioz' opera ``Les Troyens.'' You will recognize the female etoiles by the tiaras they wear, and the male etoiles by their all-white clothing.
They do this every year. It really emphasized the role of tradition in Ballet, particularly at Paris Opera Ballet, which is the oldest ballet company in the world, with origins dating back to 1669. The grand d?fil? is such a big deal that it's broadcast live on French TV every year at the opening of the season. I always find it pretty thrilling.https://www.youtube.com/watch?v=plUhhsKaC4Y