Threatening Roommate

My question involves a roommate in the State of: California

My friend recently gave a 30-day notice to her roommate to let her know that she would be vacating the premises. The roommate's name is on the lease and she took a security deposit when my friend moved in. The roommate was very upset at my friend's departure and asked that she stay an extra month until she found a replacement. On saying no to this, the roommate said (via a male friend who sent her threatening voicemail messages) she would have her and her boyfriend (who does not live there) deported unless she commits to another month, and, furthermore, is refusing to return the security deposit. My friend has secured another apartment and has to move out at the end of the month. All agreements between the 2 were verbal. What kind of recourse does my friend have on this?

Is your friend here illegally?

If she's not, she can safely ignore her soon to be former roommate. If she is, she needs to tread lightly and consider consulting an attorney if the soon to be former roommate turns her in to the authorities.

With respect to other recourse, I can't tell if your friend is in violation of the terms of her agreement. Was it a month to month agreement, or was she expected to rent for a specified period of time?

If it was month to month and she gave proper written notice, the soon to be former roommate is obligated by law to return the security deposit within 21 days.

Please tell your friend to never, never, ever rent without a written lease agreement. Those exist as much for the protection of the tenant as they do for landlords to be able to set rules.