That was a gift from the French, its irreplacable. Although, we DID ALTER IT. Origianlly it was a black woman showing we abolished slavery (of that form). However, WE designed the WTC. WE can change it if we wish :/.
Also if it was rebuilt differently, it would be to reflect the times, just as the altered version did. However, if we had the original up there and it got destroyed, then well, you'd have to the French want it to be rebuilt differntly.