Don't know their laws but in other places, if she gives him the property back before she dies in a form of gift, there's no tax cause he's her son.It's also dumb, he's gonna have a lot of inheritance tax to pay...
I think what he did is smart (for him, I'm not getting into moral aspects now) probably knew from start he could be divorced and did it to protect himself. Now, if he did it after she filed for divorce it would've been easier for her to demand the transactions to be annulled (on grounds of his obvious intent to keep his property away from her).
But, if he did this from the beginning, as it's speculated, it will be more difficult for her to get his money, at least what she demands (more than half). Though she might claim that she's entitled to half what he's earned after they got married and demand annulment of his transactions towards his mom anyway.
In the West, what he did wouldn't fly. But in Morocco, maybe.