system might have had some safeguards.

For instance it was not unheard of that other family members supported them, as we see the Austen women being set up in a cottage of their own.
Lady Russel would be there for them too, I think.

But, yes, it is very remiss of him to not think of their future. he is not even aware of Elizabeth's predicament, who cannot look at the book anymore because she is reminded of her age, and her father is not aware of it.
Makes one wonder how close they were in reality.