I'm very sorry to hear this.
In terms of letting your therapist know - you could phone them and tell them, if you feel up to it, or leave a voicemail? Or if you don't feel up to speaking to your therapist right now, perhaps you have someone else, friend or family member perhaps, who could do this for you?
When I had a recent and sudden bereavement I texted my therapist what had happened and then he called me straight back.
Wishing you all the best.