We definitely need the money. If we want to run this as a school, we need to support the students. That means getting the Ministry's money, change it into muggle money and use it to furnish what we need. We will also need it if we want to restart trade with foreign countries. No one will be dealing with us if we're knutless.
We'll see if the goblins are even there. If not, I broke into Gringotts at seventeen, I can do it again. Ron and I are expert at it.