I agree with the sentiment on here that unless you never deconstructed the indoctrination, you can't be in a position to be re-indoctrinated.
A good friend that I grew up with is an example of this. Born-in JW, but he has been pretty much inactive for the past 10 years. Has a job which allows him to travel a lot. Lives it up...resorts, partying, smoking, many tales of long nights with exotic women, etc. But keeps all this secret from his family...all JWs. Yet...when talking to him not too long ago, the subject of setting up a Christmas tree with my wife sent him into full attack mode. "So you're an apostate then?"
Caught me off guard. I don't consider him a JW, but yet he has never really questioned anything he was taught. He still believes it all, just doesn't live it. Find that kind of behavior odd...but then again, he is still indoctrinated.
However, if one has gone thru the deconstruction of their previous indoctrination, I don't think it is possible to be re-indoctrinated. Brain trauma injuries or amnesia aside.