Does smoking hashish for the purpose of prolonging sexual intercourse expel a Muslim from the mercy of Allah and invalidate good deeds, knowing his severe remorse and fear that his prayers and 'Umrah will not be accepted?

One of the reasons for the lifting of sin is forgetfulness. So, whoever falls into disobedience to Allah out of forgetfulness will not be held accountable by Allah. If your friend is truthful in his claim of forgetfulness when consuming hashish, then there is nothing against him. But if he is not truthful, then he has committed a sin and must repent to Allah.