"Where there is no prophecy, the people cast off restraint, but happy are those who keep the law" (Proverbs 29:18).
The question here, I think, is what exactly is meant by 'prophecy'? The surrounding verses offer variations on a single theme: negative choices bring negative results; loving choices bring positive results. So I understand 'prophecy' to be descriptive of the traditional role of Jewish prophets—reminding the Hebrews of that central Truth, particularly as it related to issues and challenges in their (individual and collective) lives.
Today we don't necessarily look for a 'prophet' (at least not all of us!). We find that elevated spiritual awareness within ourselves. If we ignore it we may 'cast off restraint,' but the results will not be loving and good. We are truly 'blessed' when we make all our choices from an awareness of spiritual Truth.