The film had its premiere at the Toronto International Film Festival on Thursday night, and according to Recapped (link below), Wiig's nude scene is intact.
A little over an hour into Welcome to Me, there is a montage of Kristen Wiig in her hotel room. Kristen is wearing an unfastened bathrobe and we see brief glimpses of her naked body as she moves around. Kristen then goes down to the casino floor and we see her breasts from the side as she removes her robe. We then see her full frontal nude for a few seconds before she is apprehended by security.
So there you have it. The film does not have a release date yet, but we imagine they'll try to get it released before the end of the year for awards consideration, and you should expect to see Kristen up for an Anatomy Award as well if this pans out.
Via Recapped