Money would have to be on the 400th test player to be a bowler. The next five players would probably play within 18 months, and I can't see Punter, Haydos, Langer retiring, and Hodge and Hussey could be around for a while as well (As long as the form holds).
McGrath is almost 50, Warne is the same... won't last forever
Brett Dorey looks the goods, though probably before 400. Cullen the same ...
So it would be a bowler, unless "injury" gives someone a chance.