Either you can wait and hope for a fix or get a refund now. You can't refuse to return the item and instead demand that he has to fix the issue. If it was easy to fix, it would have happened already. Perhaps it will never be fixed which is also fine in my book as long as he is willing to refund the people who can't use what they bought.
For VW, it has also been discussed that they should buy back cars from their customers if they could not come up with a proper solution. It may be impossible to find a fix or more expensive than to just refund all the offended customers.