This probably isn't what will happen, but I thought it was a fun theory:

What if Brett Partridge WAS Red John, and the Tyger Tyger group killed him before Patrick could get to him?

This would lead to more seasons of "The Mentalist" because then Patrick could shift his focus from Red John, to taking down the secret organization in law enforcement that denied him of his revenge against RJ.

It's a long shot, but I thought it was a fun theory