I really liked Max. He was the focus of the sixth movie, and I liked how he knew so much about Pokemon. Sadly, his leaving was a necessity...he was reaching the age of a trainer, so he was no longer useful as the 'little kid.'
I hope that they show Max getting back his Ralts. Now that D/P has that branch evolution of Kirlia, maybe they'll show him battling with it. In the meantime, Ash needs a new cast to work around. (As much as you hate it, Brock is the only character who was available for this stint. May had to go to Johto to compete with her rivals, and Max had to get ready to start his own journey. Brock had no attachments.)
I'm going to probably paste Max's mug shot on every page of my site, but I'm not going to cry too hard. It's like my kitten running away and never coming back. It's pointless to cry over the fate of our characters.