My guess is Roy's at 0 exactly. Conscious but pretty much unable to do anything. Of course it's hard to tell from the single panel in which we can see him, and also because we don't generally get told what character HPs are currently at anyways.
It's not Goblins webcomic (which always shows negative hp). I think he's in the negatives, and I can no longer recall the 3.x rules for not bleeding to death.
Of course, in the arena, they probably have people with the Heal skill to fix that pesky problem, and I suspect General Tarquin won't order Roy's death.
Roy should just get a second wind and kick the tar out of Thog. Seriously, I'm sick of the "it's cool to be a moron" meme. Thog and Belkar can both be tossed in to the wood chipper as far as I'm concerned.