I don’t think the Princesses could get by without a de Harry was always going to be a working royal but he could have stayed in the Army if he wanted but there was no real promotion open to him that he would have wanted. Didn’t want paper work.
In reality as long as their jobs did not involve making money because you’re royal I think they are fine.
well If Harry had decided he hated the idea of being a working royal, and said he wanted to give it up, its true he coudl have stayed in the amry for his whole career and retired at the end of it and maybe dedicated himself then to servicemen and womens' charities. But he did not want to do a desk job.