Michael Kirkland is the only one with the correct age and physical attributes and from Carson Springs.  Bob Kirkland asked each of the people that he killed if they recognized him indicating that he believed that his brother Michael was alive at minimum.  If this story, cleans up its loose ends then Kirkland has to come back into the story.

Alternately,  Red John is a collection of people in the sense that these people have been proven to specifically have done deeds for Red John.  With a large group of contributors,  Red John is in a bigger sense the Blake Association.

Patrick Jane is a Red John on several episodes in that he chooses people to be murdered by Red John.  This makes him at least a temporary "Red John"

Last note is that the Patrick Jane character was smiling when he said he was letting it go, referring to Red John.