It's reported that the remainder of the Rau collection, which he left to Unicef, is going to be sold by Sotheby's, Bonhams and Lempertz. It's a mixed bag, but the highlight is the stunning Fragonard, above, from the series of Portraits de Fantaisie, which Rau bought at auction in the 1970s for a very high price. The Louvre has several, and the National Gallery of Art in Washington D.C. bought The Reader from the auction of the Erickson Collection (from which the Met bought Rembrandt's Aristotle Contemplating the Bust of Homer for a record price). Others are in the Clark Art Institute in Williamstown Massachusetts and the Art Institute of Chicago.
The Unicef site indicates that it will be sold by Bonhams - in which case it will surely establish a new record for that auction house. It was previously on loan to the Getty, and it would be a great acquisition for them, complementing the impressive newly discovered Watteau that they bought recently. Cleveland is another plausible institutional buyer. I suspect the Kimbell, another museum with deep pockets, will struggle to compete after recently buying expensive paintings by Poussin and attributed to Michelangelo (and they're completing a building project, too). I'd love to see it in National Gallery. It's obviously an impossible acquisition for them, but their collection of French eighteenth century art is weak (the good stuff is in the Wallace Collection), and there's nothing quite like this in any British collection.