Doors that dont open on a power failure sound super fucking unsafe. Looks like on the Model s they do open manually in front if you pull the handle back enough and in the back via a hidden release cable under the seat which sounds less than ideal. I'm not sure if this is the case with the other models.
The Model 3 has a manual emergency release in the armrest: it's one of the more awkward parts of the car, actually, because it's right where most people expect the door handle to be and the actual "door handle" is a button a little bit up.