The closest thing I can remember to "automatic reinstatement" was when the teaching on "Approved Associates" was reversed. When I was a teenager there was a system whereby an unbaptized kid could be announced as a "disapproved associate." if they did something worthy of disfellowshipping. So there were a number of kids who were labeled from the platform as "disapproved associates" for stealing, vandlizing, having sex, even participating in Model UN in high school. They were treated like disfellowshipped witnesses. You couldn't say a greeting to them.
Then, one day, there was a WT article that changed all that and we could talk to those kids again. Instantly! No hearing, no nothing.
PS- This policy really jacked up some kids. Imagine not being able to talk to all of your buds at the hall- and really believing that you would probably die at Armageddon. Drug abuse, suicidal tendancies, etc often followed kids who had this policy applied to them.