The sculptor's work has technically lasted longer, but the two works are intimately connected; the state of one is symbolic of the other.
When the powerful king Ozymandias ordered this monument to be built, he told the sculptor to include these words:
My name is Ozymandias, King of Kings;
Look on my Works, ye Mighty, and despair!
In other words, the king's monument was meant to remind everyone of his everlasting legacy. It was meant to invoke awe in the viewer. Instead, the sculpture is in ruins, as is the legacy of Ozymandias, by association.
At the end of the poem, the traveller remarks,
Nothing beside remains. Round the decay
Of that colossal Wreck, boundless and bare
The lone and level sands stretch far away
The monument is now in a state of "decay" and is even a "colossal Wreck," so clearly, the legacy of Ozymandias has not lived on in the glory he had imagined, nor has the monument itself. The irony
of the poem is in the juxtaposition of Ozymandias's proud words and the disarray of his monument. While more of the sculpture remains than the great "Works" of the king, neither has endured well.