I see. That sounds serious if you fear for your personal safety
You may wish to seek a restraining order against the individual and report the issue to the police if he has made threats against you. If you obtain a restraining order, he will typically be prevented from having any contact with you and the employer must accommodate you in some manner.
If HR is unwilling to aid you in resolving the situation, it really would be best if you retain a local employment law
attorney to communicate a demand to the individual who is threatening you that legal action will be taken if they do not cease engaging in such conduct.
If you have requested FMLA leave, that federal law protects you from termination
by the employer for taking FMLA leave and they must protect your job until you return to work.
Ultimately, the employer could terminate you or the other employee unless there is a contract stating otherwise, but if you retain an attorney, it is more likely the employer will act reasonably and actually punish the one at fault--the other employee--and not you.
I hope this helps clarify the situation for you. Please remember to rate my service once you have all the information you need so I will be compensated for my time from the deposit you posted with this website. If you have any other questions, please ask me – I’ll be happy to respond. Thank you!