I have a great inheritance from the previous owner who seemed to do everything super poorly, I have to skim coat over terrible texture but ran into this. It's bowing slightly away from the room above the header. Will sanding and skimming this over be enough or time to bust out the saw?
The crack will show back up in short time if you just skim coat over it. Id take a utility knife and cut out the crack (v notch). When you do this the reason it cracked could reveal itself. It could be that the previous guy didn't tape properly. If that's the case fill up the cut out crack with hot mud. Tape it with all purpose mud (id use Fibafuse Tape). Then finishing coats use plus 3. However depending on what you find you might just need to replace a small section of drywall.