Hey LFM,
We don't know for sure what exactly happened to Mitch. Some believe that he immigrated into a neighboring wild group. Others are not so sure.
He was well into roving age when he dispersed from the Whiskers, so chances are he left the group and either..
1) Start his own group
2) Immigrate into another one.
However, none the less even if the researchers of the KMP found him after that, it would have been long after his dye marks faded, making it difficult for them to identify him (unless they checked his ID chip). I have every reason to believe that Mitch is still out there (that is if he's managed to avoid predators, vicious fights from neighboring groups, poison from a snake or some other means, and of course the dreaded TB and other diseases/starvation

) And I know MM made up quite a bit of stuff in the storyline, but with Mitch I don't think they were exaggerating. I think he had all that it takes to survive in the Kalahari

Because he was a male (and I hate to say this) he had a much better chance of surviving than evicted females do. Other mobs rarely accept other females into their group as there is too much competition between the ladies already. Males however, have a much better chance.