Zidane has played many young players, I don't think he'd have a problem in rebuilding.
That being said, if he fails this year I can see him leaving (or agreeing with Perez) on his own as to keep his legacy.
But he hasn't built the core really. He made two key changes with permanent introduction of Casemiro and allowed Isco to make it through in Bale's absence, which brought balance and spark that lifted RM into a complete domination calibre in Europe. That's what was so important, because half the results last year came simply based off of confidence. He hasn't had to deal with the actual major shift yet, still probably sees Modrić-Kroos as a duo to lead for another 1-2 years when in reality Luka needs serious management already while Kova is somebody who makes runs from deep as his main weapon, but doesn't distribute in tight space nearly as well. Ceballos has that game, but isn't trusted.
In essence, no trophies will mean heads will roll. And with that sort of squad and unhealthy family-like relationship that it's turned into, it's usually the weaker squad members that get replaced to shift the blame i.e. keepers (Kepa rumors), rotation strikers (unyielding search for a dude who wouldn't replace the crappy Benz but would be good enough to provide bench support when required), rotation fullbacks and DM (Marcelo, Carva and Casemiro having no perceived competition will be highlighted and Theo, Llorente or Hakimi could actually be allowed to leave). Also, there'll be one big signing at least. Whether it's some form of a Neymar agreement or Hazard (Zidane likes the guy, sadly).
The right thing to do would be to throw the kids out there far more often now, even if PSG would end up being a humiliation. There is nothing that hints on the change in regularity of results from the current team aside from Bale who constantly outperforms everybody this season.
It's just a tad shit this year, but not the end of the world for me really. Zidane has instilled such attitude in a section of fans that are grateful for 4-6 years of success during his tenure in the club. The other section are the traditionalists who push for constant trophies. It's more of an internal war between the two camps ATM.