I do agree with your comical ending point about there being a lack of gardeners that will be produced out of Generation Z. In their defense though I will say that I have never met any teenager or even a person in there twenties that just took up gardening as their hobby. That may be something that as a person grows older may steadily become more of a recreational hobby. I do believe the country came down to where all had to live off the land those of Generation Z would end up figuring out how to live off the land.
Yes this generation is bound to its technologies such as phones and computers, and yes at times they make the generation look needy or even like “morons and imbeciles”. If it really came down to this Generation Z having to figure out something such as gardening without the use of technology I do believe it would be a bit of a tough transition. In the end they would prevail and overcome just as previous generations have when they were “imbeciles” for having their latest technology that made them less efficient than previous generations. The technologies we create are helping us more than they hurt, but if we were to ever lose them and depend on the land for survival they would prevail.
Chances of "survival" follow the story of "The three Little Pigs" quite well with "The Greatest Generation" building the house of brick and "Generation Z" building a house of straw.