I brought mine "forward" into adulthood rather than going backwards. If one is coping well I don't think one will uncope? If one regresses, they probably had various behaviors that were tell-tale from before or, the situation causing the regression was extremely stressful (death, breakup, etc. so one goes into a fetal position, for example).

Have you seen that show, "My Strange Addiction"? http://tlc.howstuffworks.com/tv/my-strange-addiction They had one with a 22 year old woman who still sucks her thumb (with a piece of her baby blanket rubbing against her nose).