Why should they? Football is a game where injuries happen. If he blows out a knee or a spine or whatever and can never play football again, that's just the nature of the game.
The three year rule is meant to minimize these permanent types of injuries. If he wins the case and gets to play early, I'd be expecting him to get sidelined permanently with some injury. He's just not physically mature enough yet.
And he is hardly a scab....I have read numerous statements by NFL players that say Clarett should be able to play.