I am almost sure that he will not go to Saudi Arabia 
Mbappe is a football player who pursues his dreams at a young age. If he is determined to go to Real Madrid, no team can take him. I think he will play for PSG one more year.
Saudi Arabia may well be a real option for the transition stage before the end of Mbappe's agreement with Paris Saint-Germain, no matter how fantastic it would have sounded six months ago. At least there seems to be such an offer from the Saudis to invite Mbappe to Saudi Arabia for a year, given the damaged relations between the PSG leadership and the player. Then PSG would get money for rent, and the player would get game practice, and I'm also not sure that Luis Enrique is excited about the idea of building the future of the team around a player who will leave after a season. Mbappe is a football player who pursues his dreams at a young age. If he is determined to go to Real Madrid, no team can take him. I think he will play for PSG one more year.Mbappe is still smart enough I guess in this regard so there is no such option if indeed he still wants to be recognised with his performance and he still has to learn from his previous mistakes when looking at money rather than achievements and a good level of competition. Even if he does see money it is still valid and there is nothing wrong with that but he must also realise that his career can be more than that.