Truth be told, Watson may miss far less time than Kamara. A grand jury opted not to press criminal charges against him. At the moment, there are 4 civil cases against him. The other 20 were settled out of court, and therefore, in the eyes of the court don't count for anything, especially as they came with a gag order for the plaintiffs.
Not only may Kamara's suspension be similar to Watson's, there's a very real possibility of a jail sentence, as he's charged with "felony assault, resulting in grievous bodily injury" (or words to that effect). From all media accounts, the evidence against him is pretty ironclad. The evidence against Watson is not as damning. While reprehensible, a good attorney could poke holes in many witnesses' testimony, or damage their credibility by tarnishing their character.
I wouldn't be opposed to a trade for a quality RB as an insurance policy, unless the coaches like what they have in Abram Smith, and they believe that Ingram still has enough gas in the tank.