Does anyone know what the ethical expectations are for continuity of care in a situation where a therapist suddenly becomes unable to see clients?

I've read a little on professional wills, which ensure that there is someone to contact clients in these events and provide notification that the therapist is unavailable as well as referrals for other therapists, temporarily or permanently. What I've read also mentions that failure to do this could be considered abandonment.

Does anyone have any insight on this?