What is required to fix this plastered drywall ceiling?
This was a nice straight plaster ceiling and I'm assuming you want it to look that way again. I would be sinking those drywall screw to the drywall level, add the drywall to the still damaged area and the plaster over the whole area. If some of the old plaster is loose, break it away first. This should give you a smooth finish to the rest of the wall. I think taping it would be really hard to hide.