I live in Louisville, KY. Zone 6. I have a newly planted baby black bamboo plant in a large pot. I'm curious if I don't bring it in in the winter if this will completely die out and I'll have to start it over again in the spring or if it will stay alive?
The problem is its in a pot, which makes it much more vulnerable to cold in the winter. If you insulate the pot well, you might get it to survive, but if it gets cold enough for the whole pot to freeze solid, then it'll die, and in your Zone, it just might get cold enough. Stacking bales of hay round a pot won't be an attractive sight all winter, but it might work.
Based on the USDA Plant Hardiness Zone Map you are very close to the critical temperature for Black Bamboo. It suggests an average annual low of 0 to -5. The resources I can find say it can't handle much below 5 degrees. Above 5 it's fine, below -5 it's probably dead. In between you get varying degrees of cold stress that won't quite kill it, but will likely weaken and injure it.
You would need to insulate the pot very heavily, and (if possible) try moving the pot to a more sheltered location for winter. Unprotected, an unusually cold winter will likely kill it.