My understanding is that pure carbon things sublimate into CO2 over time (including diamonds) when exposed to oxygen.
I don't disagree that this might happen, but isn't this usually called oxidation and not sublimation? Sublimation refers to a state change (always C), and oxidation is a chemical reaction (C to CO2). If oxidation happens quickly enough, I heard it is called "burning"...
At any rate, you are partially correct in that diamond oxidation depends on sublimation occurring:
But you may need to heat it to 350 degrees C for this to happen at a noticeable rate: