Someone can always sue. The question is whether they can win.
If you made a truthful report for a legitimate reason, then you would not be liable for defamation. (By the way, libel refers to a written statement. Slander refers to an oral statement. Defamation is the broader term that encompasses both libel and slander.)
Here, your accusation was legitimate if you felt threatened by your co-employee. If it is true that this person was making threats to you, you had an absolute right to report this. If your report was accurate, then you should have no liability.
In addition, I assume you reported this to your employer. If this is the case, your employer has a duty to investigate and take the appropriate actions against the person who threatened you.
Most homeowner's policies include personal liability coverage. Some of these policies will cover defamation claims, especially if you have an additional "personal and advertising injury" coverage. Strange, but true, that your homeowner's policy can include this type of coverage unrelated to your home. Insurance companies decided long ago to bundle these two types of coverage together and offer them as a single product, although I could not tell you why. Same with renter's policies.
However, even where the policy language would seem to permit coverage, insurance companies differ in how they respond to defamation claims. Many will deny coverage on the basis that defamation is an intentional act, and therefore not insurable under California law.