Little hints remain in the series indicating that it's not over with RJ saga -- like the fact that Jane still wears his wedding ring as a promise to his wife and daughter to find justice for them -- which doesn't make a lick of sense if the real RJ is REALLY dead and gone.  It's been over two years now.  Seems reasonable to think that ANYONE would want to start moving on after a decade of pain and searching, and two years on an island where you don't speak the language... 

Jane is pretending to believe that he's killed Red John...

because...JANE GIVES THE VILLAIN WHAT THEY WANT AND EXPECT...FOR A TIME...before he reveals his true intention and knowledge of their crime, finally capturing them.  When he captures them -- he needs PROOF.  You can't just implicate someone and expect to succeed.  They have to be caught "RED HANDED"  :p

Villain is usually arrogant enough to believe they've gotten away with it, tricked everyone -- that they're smarter than others, which is precisely when they'll make mistakes -- RED JOHN is NO DIFFERENT, just a villain requiring a lot longer time in terms of obtaining real proof.