If the price is right, he'll be sold.
Someone mentioned merchandising as a reason for Juve keeping him. Fans will buy Juve gear no matter who is on the team, so that theory doesn't hold water, whether DP is here or not.
It all comes down to quality of play on the field, and are they unequivicably a better team with Alex on the field than off of it. It has been pretty hard this year to determine that since he has missed so much time, but the fact of the matter is, the older he gets, the more injury prone he becomes, and if defenders are going to keep mauling him every time he touches the ball, then he may never be truly injury free again, at least not in Serie A.
Its also very possible that he has lost a step, which is why defenders are able to catch up to him and make life miserable. If they had better attacking midfielders it could make life a lot easier for everyone involved.
maybe, just maybe, the question is not should DP be sold, but should Nedved be sold instead?
His play has dropped considerably this year, and he's also two years older. The difference is that there are a lot of teams who are tantalized by the prospect of having a ballon d'or winner on their team, and therefore would pay a higher price for someone (Nedved) who may be even further on the downward slope than some others (DP).