Is it permissible, from a Sharia perspective, for me to help a wife return to her husband who does not pray, is addicted to alcohol, and frequently curses Allah, given that I am able to do so?

Slandering Allah the Almighty is an act of disbelief that expels one from the faith, and there is no excuse for anyone to do so. The ruler must demand repentance from the one who slanders; if he repents, then good, otherwise, he is to be executed.

The one who slandered is separated from his wife, and the marital bond is suspended until the 'iddah (waiting period) ends. If he returns to Islam, his wife is restored to him. If the 'iddah ends, then the marriage contract is annulled.

Regarding abandoning prayer: If it is out of denial of its obligatory nature, then it is disbelief by consensus. If it is due to laziness, then there is a difference of opinion among scholars. Some consider it an act of disbelief to intentionally abandon even one obligatory prayer without an excuse until its time expires.

This person must be called to repent from his actions and renew his Islam. If he repents, re-enters Islam, and establishes prayer, his wife is returned to him. Otherwise, they are to be separated.