Size is relative. A large active order with 90% of their order over 65 years of age, which depends on the salaries the sisters make (as hospital workers, teachers, professors, principals, DREs, parish administrators, etc) are going to have serious financial problems when they all retire.
But smaller communities with a healthy amount of new, young vocations, which depends on donations may be around for a very long time.
The main concern for finances is how the order raises the majority of it’s money. Do they lease out farm land (like the one in Central PA that was objecting to the pipeline), do they run a college where the college pays for their mother house and expenses? Or do they depend on the work of individual sisters?