You cant be certain. The transfer window is still long. A lot can happen in a month. If Mbappe doesn't want to sign a new deal, PSG can be forced to sell him and use the money to strengthen their squad. Madrid will not buy Mbappe for the amount PSG are asking for. Personally, I feel if Mbappe wants to go then PSG should let him leave to Madrid, but if they can convince him to stay for one more season, they should. That would give them enough time to look for replacements that can step in and replace Mbappe. PSG do not want to sell Mbappe because they do not want to lose all three of their top players. Messi has left, Neymar would most likely leave, so losing Mbappe would be a huge blow for them.
I am not sure that Paris Saint-Germain does not want to sell Mbappe so much, knowing at the same time that he will leave next year as a free agent 
On the contrary, PSG REALLY wants to sell Mbappe right now because of this, while it is possible to get about 200-300 million euros for him. Even more Paris Saint-Germain would like Mbappe to extend his contract with the club for another couple of seasons, but before that I thought that from the field of unscientific fiction like fantasy, but the latest news about Mbappe requesting 240 million payments from Real Madrid is beginning to make me believe that probing the possibility of extending has already begun on his part a contract with PSG, because Real Madrid is hardly ready and willing to pay such sums to a player.