It is not the end of the world, but the trustee will scowl at you.
If your bank has closed the account, we will simply tell the trustee that you were not able to get a printout of the balance on the date of filing. He will grumble and then direct you to get a letter from the bank showing that the account was closed and showing the ending balance.
Sometimes, the trustee will even take your oral testimony that the bank account was closed, although this usually only happens when the attorney can point to some other cross-collaterized loan you had with the bank that you are also bankrupting.
That being said, if the bank is still mailing you paper statements, then the last paper statement should show the balance that the trustee’s is looking for.