Del Piero can't be a winger in a 4-3-3.
I'll trust you on that, but then again, 4-3-3 is just a way to describe a formation. He won't necessarily be stuck on a wing, if you understand what I mean.
This is how he played with Parma in the final games of the season:
Castellini, Contini, Couto, Coly
Parravicini, Cigarini, Dessena
Rossi, Budan, Muslimovic
If Trezeguet leaves, it is possible that Iaquinta is brought in as a target man (Budan). He might not score 20+ goals, but I do think he makes a better target man than David. And Rossi does remind me of Del Piero. He's hardly a winger but has still been very succesful in his position.
As Vonam said, rather than having two pure wingers, it's more of a christmas tree formation.