They cannot just return to the congregation as the elders decide on how long a person remains disfellowshipped. For instance if you confessed to fornication and are disfellowshipped and never do that sin again the elders may reinstate you, meaning people can talk to you again in six, nine, twelve months or whatever they deem. The shortest I have personally seen is nine months. As far as the verses read to you they do not follow that procedure for what they consider serious sins. The elders will always form a judicial committee for what they consider serious sins even if as the scripture says the person listens.
A very serious sin is disagreeing publicly with the organization or some doctrine. You will be disfellowshipped for those reasons. If you think that disfellowshipping is fine than so be it. But I will run another scenario by you. A child raised a witness gets baptized at 14 and at 16 likes a boy. They mess around and commit pornea by watchtower standard definition and are both disfellowshipped. At 16 they can no longer speak to anyone they know.
or at the same age they start researching and discover things they don't believe in. If they vocalize these to the elders the child will be disfellowshipped at 16 or whatever age they are at the time. They are forced to profess they believe JW doctrine to ever be reinstated to be able to talk to the people they know again.