If someone in a bipolar manic episode threatens to kill you, will the carry out the act?

Can't be sure: While the mentally ill on the whole are not especially prone to violence, any explicit threat must be taken seriously — especially from someone with obviously poor judgment. A person at risk for endangering himself or others (eg, threatening to kill) due to a mental disorder can be held for a psychiatric evaluation and protective custody. Call 911 if you feel unsafe.

Take it seriously: Part of the stigma of mental illness is that the mentally ill are predisposed to violence. It is actually a far smaller number of those diagnosed and violent than not diagnosed and violent. I recommend taking any threat of bodily injury, safety, or death seriously. It is a crime to threaten to kill someone and the incident should be reported to the police.