I have checked a number of U.K. stockists including the Fuji film site itself and there was no sign of Pro 800 but neither was there a notice saying "discontinued". It is still available at one stockist with a stock plenty listing but that stockist may simply have put in a massive order prior to its discontinuation( if this is the case).
It would appear however that Superia 800 is still a product line and 1600. The latter is very fast but gets a bit grainy above 10x8 in my experience.
So a bit of a mystery. There seems to be some evidence that Pro800 may have been discontinued but it is not conclusive.