Paintings, like most other pieces of art, sometimes are sold by the museums that own them. This is why pieces, like some art by Van Gogh have recently been sold for more than $10 million.
Having said that, it only proves the old saying that almost anything is for sale.
The Mona Lisa is not only famous, but, due to the recent Hollywood films, very popular. Also, the Louvre in Paris is not in any financial difficulty, so the real question at the moment, is whether there would be any reason for the Mona Lisa to be sold.
To decide whether the loss of this painting by the Louvre would bring a net financial gain or net financial loss means answering the question of whether an immediate input of $10million or even $100million would offset the adverse publicity of "losing" the Mona Lisa.
I believe that today, with the popularity of the DaVinci Code, and other recent films and books, the world and, I believe, all of the French people, expect the Mona Lisa to remain in the Louvre forever.
Therefore, I do not believe that e Mona Lisa could be purchased at this time. Perhaps 10 years ago, when the painting was not as popular as it is today, a purchase could be negotiated. Also, if the publicity fades as fast as most things in today's world, perhaps 10 years from now, a purchase could be made at a fair price.
In the meantime, I do not believe that it would be anything to evpect that the Mona Lisa would be sold, except on the possibility of the total collapse of the economy of France, which is not expected, since France has the financial backing of the European Union.