Mom (80) won't get verbally abusive son (54) out of her assisted living apartment?

Why is the assisted living allowing this? Is his name on the lease too? This is wrong on so many levels. Your friend needs to address this with the administrator and director of nursing at the AL. Between the three of them, a plan of action for eviction needs to be in place. Also, contacting the long term ombudsman asap is a good move. This way, there is documentation to start.

Usually Assisted Living facilities have just a studio apartment for their residents. Where does he sleep, and does he eat in the common dining area with the other residents?

This is so messed up as to almost sound like a hornet's nest...that you wouldn't want to poke. If you can't talk him into moving...and she doesn't want to force him...if the assisted living facility doesn't care...the only option is nuclear.

I would be hesitant, frankly. The nuclear option would be to declare mom incompetent and evict him. I think that's a poor move. It's liable to produce very unpleasant unintended consequences.