Directly? Probably not. But, had Harbaugh still been there, would those players have left? Would they have stuck around knowing that the team was very good and had a realistic chance to win it all? With him gone, can the same statement be made? I'm not sure, but am also not optimistic.
Harbaugh and the front office had major personality conflicts. I firmly believe that the FO leaked all the crap that went on last year in an effort to get him out. They knew that by bringing instability to the team they would falter and make it easier to can him.
Well they got what they wanted. He's out. They got a company man to replace him. Is Tomsula a good coach? Yes, as a DL coach. As a head coach, other than 1 year in NFL Europe and 1 game in the NFL, we don't know. But given the York's track record of hiring head coaches (Erickson, Nolan, Singletary, Harbaugh) it's not looking good. 1 out of 4 is not good odds.