I don't really understand what point you're trying to make here. Do you have some experience with or knowledge of the banking sector? If you have some practical knowledge of how the banks go about reclaiming money in this situation, please state it. I admit I don't know how it actually works, so I'm happy for you to enlighten me. Otherwise, however, you're not really making any substantive contribution here.
The key point in the context of this thread is that the OP is not entitled to spend the money. Yes, it may be difficult for the bank to retrieve money he's already spent, but that doesn't change the fact that he's committed a criminal offence in doing so, nor does it mean that there won't be considerable efforts made by the bank to reclaim said funds.
This thread has been rumbling on because of a basic misunderstanding about the law and a naivete by some posters that has led them to think that they can just profit from accidental windfalls. If a large sum of money belonging to another person or entity inadvertently ends up in your possession, you don't think that that person or entity will do everything in their power to get it back?