Does the husband's leaving the home and telling the wife's mother, "Tell her that I am done with her and she is done with me," constitute a divorce, and does his resorting to sorcerers and neglecting prayer expel him from Islam, knowing that he has repented?

First: Going to sorcerers and soothsayers is among the major sins, and it can reach the level of disbelief (kufr) if one believes their claims about knowledge of the unseen. If a person was ignorant of the ruling, we hope they are excused. However, for someone who knows the prohibition, it may lead to their exit from Islam.

Second: Scholars have differed regarding the disbelief (kufr) of one who abandons prayer out of laziness. The preponderant opinion on this website is that it constitutes disbelief.

Third: A man's statement to his wife, "I am done with her, and she is done with me," does not count as a divorce unless the husband intended divorce by it. Since your husband has repented and returned to his senses, you should open a new chapter with him.