Fortunately, initial reports of Briggs' condition were off; he suffered no brain injury. He does have a broken orbital bone, nose, and torn bicep tendon.
It should never be the job of the fighter to know if or when to stop a fight -- that's both a distraction and an affront to their dignity. A fighter's job is to fight to the best of their ability, and if they've been trained properly both physically and psychologically, they will keep fighting regardless of circumstances. Which is why it's incumbent upon the corner and the ref to think of the fighter's well-being for them.
First half of the fight Briggs remained fresh enough despite taking some good shots, and hunting for an angle; he was never effective offensively. By the second half he was tiring, eating a lot of rights, and mostly just trying not to get knocked out.
He looked incredibly tough, more so than I recall ever seeing or expecting of him before, and there was never a moment where I was disgusted that the fight wasn't stopped, but there were many moments (and rounds) where it would have been fine to do so. Toward the last couple rounds, it would have been right to do so.
It's my tendency to blame corners first, and refs second, and that stands here.
And Klitchko, frankly, didn't look very good either -- neither particularly fast, sharp or powerful, just more of an edge but only by comparison. Overall both looked older, heavier, slower and sloppier.
Fight can be seen here; scroll down to Saturday, 4:50pm: