Although there's certainly more to say, especially with regards to agricultural productivity in late antiquity and the fall of the Empire's impact on the mediterranean "common market" for agricultural goods, we've actually gotten a number of questions about the end of Rome recently that might give you a cleared idea about life during the end of the Roman Empire.

This discussion led by u/Iguana_on_a_stick examines life in "Roman Cities" after the end of the empire, and might give you a clearer idea of what post-Roman society was like. u/shlin28 wrote this other answer on the specifics of the city of Rome after the empire ended.