One has a few variable parameters such as ‘country’, ‘agrarian’ and ‘survive’ that would allow a hypothetical construction of numerous models including futuristic ones with hyper-modern agriculture- perhaps indoors. One might have an altered demographic or political constituency that would influence the standard of living.
If a modern nation was exceptionally productive it might dominate global food sales and create a surfeit of very cheap commodities for human consumption that would keep its people alive- surviving and thriving. It is difficult to say. Traditional agrarian cultures certainly have a hard time of things these days though for it implies a lack of advance, education and the ability to afford defense weapons that are quite costly.