Once a transfer has been started by either a business or Private sale, it will still go through, even if a ban is passed into law.
As long as the Transfer was started BEFORE the Law comes into effect. The Transfer will go through.
Unless you know more then the Firearms Lawyers that have commented on this potential issue.
The lawyers are over the place.
If you get stuck with a gun and no transfer, you can always get your money back - I guess.