Darko was just another in a long line of European players that are marginal NBA players and decent European players that will go from the NBA back home and then back and forth. A lot of these guys do it. They miss being home or around family or their own culture and language.
Unless you are a superstar that decides to stay here, a lot of these Euro guys are going to wander back and forth.
Darko is marginal NBA talent. He might have helped but think of it this way: if he really left to go home to take care of his mom, then, if he had stayed, his mind clearly would not have been here and his performance would have suffered.
If, however, he left because he wasn't getting playing time, what does that say about him as a professional and is that the type of guy you would want hanging around this team influencing the other young talent on the team? Remember, not every young mind gravitates to the "KG is great and I need his mentoring" philosophy. Many could be turned off by KG and looked to be influenced, consciously or not, by other people. I would rather they gravitate to Doc or Pierce or someone else rather than someone like Darko, if he is the type of guy to quit on a team and a professional contract because he wasn't doing enough for the coach to give him playing time.
If Darko left because Doc wasn't giving him playing time, I think that says mountains more negative things about Darko than it does Doc.