There are more serious problems than physical health issues. Jehovah is said to be ready to take care of, or prevent, physical health issues in the New Dark Ages. Teeth that will not break, having forever to travel, and the like are all answers coming from the witlesses.
But, there are other issues aside the totally unbearable stagnation and tyranny that will be found there. For one thing, all the people that are educated will get destroyed. So, who is going to develop the infrastructure so people can get around? Those houses need to be designed--they are not going to just build themselves. Someone is going to have to move the materials to the building site (again, they are not going to just walk to the building site). Someone is going to have to design tools to build it. You might be able to do without locks on the doors, and they claim that Jehovah will prevent it from getting excessively hot, cold, wet, and/or windy. However, one still needs appliances if one is going to prepare food.
And, even given that crop failures are now impossible, how are they going to get crops to distant areas? We know that chocolate, coconut, palms, bananas, oranges, apples, nuts, and mangoes all grow in different areas of the world. You could not grow oranges and bananas together because oranges need cooler weather than bananas (and they need it dryer). Most tree nuts grow in temperate areas (Brazil nuts are the exception), while the chocolate that usually goes with them grow in the tropics. Coffee also grows in the tropical latitudes, at high altitudes--making transportation a nightmare.
Or, perhaps we all eat locally grown food? That means no chocolate, coffee, coconut, bananas, mangoes, Brazil nuts, or palm oil if you are in the temperate areas. (And no pineapples.) If you are in the tropics, it means no walnuts, peaches, pecans, apples, or any other fruits that grow in the temperate areas. And, if you are in the off-season in your area, you are out of luck. One could not survive until the harvest season unless one has some means to store and transport food out of the local area, and all those with that ability will have been destroyed.