Here's what I think. If he plays Del piero and Cassano together, he'll be doing something right because Italy are in dire need for players like them. However, Donadoni must be thinking about his pride too.
Playing Del piero, Cassano, and De Rossi would mean he has listened to the press and the Italian fans. In actuality, the coach of the team would then be te Italian press and fans and not Donadoni. Surely, if he does play the formation everybody wants him to play, his competence as a coach would largely be at question. Not that it isn't already.
When Capello was at Juve, everybody called for Del piero's selection but he never listened. He stuck to what he believed in despite the never ending critisizm he received. He won two Scudetti at the end though and that's why Capello is one of the most respected coaches in Italy, if not the world. It's his arrogance and authority that has earned him a great deal of admiration from many people.
Donadoni is faced with a rather difficult task here. If he sticks to his prefered formation and Italy fail to win, he would undoubtedly lose his job and would be hated by millions of Azzuri fans. If Italy do succeed, he will grow in arrogance and could possibly earn the respect of many fans, the way Capello did.
If he chooses the more sensible option and that is to pick the most in-form players at the moment, Cassano, Del piero, De Rossi etc.. and decides to drop the players and even the formation he dropped against Holland, his credibilty as a coach would largely be at question since anyone in the world can coach Italy in this case, he would just have to read the papers and see what the fans want.
For him to drop the formation he has been working with for over two years and to choose players who haven't been playing regularly for Italy for a long time(Alex and Cassano), it's not as easy as it looks because if he looses, he will be at fault for listening to the press and if he wins, he wouldn't take any of the credit.
It will be very interesting to see what type of person Donadoni is. If he is selfless and cares only for Italy, he would change his style of play and quick. If he is arrogant and cares more for pride than he does for his country he will decide to take a big gamble by playing his preferred 4-3-3 formation with the Milan trio, and the exclusion of Del piero and Cassano from the starting line-up.