I would guess that a sheepherder in paraguay who has never seen many effects from the industrial revolution ought to be minimally affected. He shouldn't get much radiation unless somebody intentionally uses cobalt bombs or such. He should be able to live just fine without new steel knives and such. I guess there would be no subtle interactions that would kill him, and I have no basis for that guess except my lack of imagination.

Unless he's part of a subsistence community (and even in underdeveloped countries most agrarian workers are not,) he's still economically tied to industrialized civilization. He's still directly or indirectly dependent on a consumer market that's now gone.