What would happen in a ballet company if one of the dancers was injured?

: What would happen in a ballet company if one of the dancers was injured?
Hello! If a ballet company was rehearsing for a production, and one of it’s dancers got seriously injured or sick, what would the company do? Would they upgrade a less-important person for the part and just leave a spot empty? Or would they employ someone new to take over?
Even if there is an understudy, surely those understudies will have to leave there own parts and leave vacancies?
Thanks very much!

Answers and Views:

Answer by SandraLAVixen
Understudies learn, both, the same choreography as the lead roles and the choreography of the ensembles.

…At least they do in a well managed dance company (hint hint).

Answer by Janine
The shuffling around does not create a vacancy because that’s why companies have apprentices. Apprentices learn the corps roles.