Not exactly a sympathetic plaintiff.
As far as the merits go, I think it's easy to allege negligence, harder to make a compelling argument for. He was a Restricted Free Agent without arbitration rights, his role in the conduct was certainly... heavily suspected [No HFBoards spec, etc. etc.] The team that held his rights didn't want to sign him, he presumably could have signed the qualifying offer [a 5 second google search and I can't find an example of a player that actually signed a QO, but it's presumably an option], nobody else chose to make an offer sheet or to put together a compelling trade package.
With all the facts and circumstances, I'm not sure how the Agent could have been negligent. Like when I think of that, I'm thinking of things like "teams were contacting the Agent to try and make offers, but he just never communicated that to his Client and never got back to the organizations, and so they lapsed costing the Client opportunities a reasonably prudent Agent would have provided". Teams don't want you because they suspect you engaged in criminal conduct isn't your Agent's fault.