The human head of the sphinx is much smaller than its lion body (proportionately; this is hard to explain but just take a look at it with this in mind)

https://en.wikipedia.org/wiki/Great_Sphinx_of_Giza#History

I am defining 'substantially recarved' thusly: the sphinx had an original head that was larger and the current human head was carved out of this. There is no requirement to clearly understand what that putative original head looked like (which means that there is no requirement for the putative original not to also have been human).

'we believe' is tricky. If, before 2040, the Wikipedia entry for the Great Sphinx says that a substantially recarved head is either generally accepted or just the most likely theory, this resolves YES (as long as the Wikipedia page has stabilised).

If, on 1.1.2040, the Wikipedia page says that this question is unclear, and that a substantially recarved head is approximately similarly credible to an original head, this will resolve to 50/50.

If, on 1.1.2040, the Wikipedia page says that we believe the current head is the original (or by omission implies this), this question resolves NO