As far as I can see the best thing PSG can do about their players like Mbappe who won't extend his contract is to keep him for another season when his contract ends and until that time they can use this player to achieve their goals. Also, PSG would use another coach and Luis Enrique can be a good option for them in the next season while they still can have Zidane as their first priority.
Do you mean to win french league again? Mbappe has been signed for something bigger than it to win UCL. Losing mbappe as free agent is a big loss for PSG. You can remember that if PSG paid a lot of money for him.
It's not even worthy of PSG paid almost 1/5 from 1 billion to win only french league. The price that already got from winning french league was smaller compared with money used to buy mbappe.
Im thinking about PSG must try to make him leave from the club by selling it. It will help PSG so much to recover some funds used to bought him.