I've never heard that. Did the emperors that followed him keep it in place? Of course, Rome was known for "bread and circuses" even long before Julian.
Discussion
Yes and no. The separation of Church and state leads to the state doing the work of God (The Church). Christianity is what brought us hospitals, orphanages, etc, and the state stands to commandeer these ideas... Obviously this topic is so deep.
Dr PATISTAS book, "The Ethics of Beauty" covers this in such a beautiful way, I certainly won't do it justice.
I don't favor the combination of church and State, as was the case in the Eastern (Orthodox) Roman Empire, aka the Byzantine Empire. I believe the State actually took over many of the societal functions the church previously performed, and, as with most everything the State does, it does a poor job of it.