Can a person who has been in icu and sedated for 4 weeks come out completely normal? like his brain not being affected by the sedation?

YES!: This is an answer given to you not only by a doctor, but also from personal experience. My husband had complications after kidney surgery in 2015. He was 5 weeks in a medically induced coma in the ICU, but came out of everything fine, even though he has MS. Please do not lose hope- they can come out of this. Also, talk to him even though he is "out". My husband reports remembering things!

Yes, very possible: Assuming no hypoxia or blood vessel obstruction, and absence of pre-existing traumatic intracranial bleeding, it is indeed possible to survive the ravages of a stay in ICU, and experience a substantial recovery over a period of several weeks.