I've managed to return back to NSA after retrieving the BioChips from all three robots. I'm now told to head to Paris to capture Sinclair. The trip there appears to be impossible, unless I return to Caldoria. I've search everywhere, the roof is still blocked off.
Is this one of those take it for granted, you'll fail type endings.

At no point in the game do you travel to Paris. The solution is on Caldoria.

The rooftop is officially blocked off, but what if you had something in your inventory that could get you in there regardless?