Zidane might reject the offer since Deschamps could leave the management of France national team after this World Cup, besides, Mbappe will leave PSG, Messi might try to leave too to Barca if possible. The team will be less competitive and will require to find substitutes for them.
Well, everything can happen. I mean, Zidane may not be interested anymore if PSG turns out to be a less competitive team. Mbappe, Neymar, Ramos, Donnarumma, or Messi has the rumor to leave PSG, I have read it several times on social media or sports news sites. If some of these key players leave PSG, surely this team becomes less competitive. But as long as the team has a plan to buy again some top players as the replacement, it won't be a big problem. The problem is when the club has no plan for new top players. If this happens, Zidane should be not interested since he knows it will be too risky for his coaching career.
Zidane would be great fit, but he'll be doing them that favor? Zidane would not come into a less competitive club with no discipline and solid attitude. He's intending to be the mentor for France national team. Replacement of Pochentino is inevitable, if Mbappe, Neymar, Messi's existence nothing to change then it'll be very hard to PSG deal the next season. Zidane is a talented, and surely won't take the risk.