Ex HOD here, left last year. Things that would need to happen to make me go back:
Make the job doable in a working week of 40hrs. So that means more adults in schools so that teachers get the time they need to prep/mark etc.
School/home contracts that are enforced. You signed to say your kid won't do x/y/z. They did it, here's the consequences and no arguments. The consequences need to be super clear. Any abusive parents are banned from site immediately and police involved (required police investment here too!)
More adults in classrooms for SEND support
More different spaces/schools for SEND pupils
Culture change in schools. I've worked in and out of schools, the work culture is ridiculous and based on guilt, "doing it for the kids" and martyrdom. It leads to burnout and people leaving. Which leads to ...
SLT need to go and work in non school environments for a while.... So many are miniature dictators, or simply incompetent and promoted way above their ability and need to sort out the way they treat their people. I have been go smacked by my new role and the fact I am treated so differently than when I was a teacher by my own managers. The way teachers are spoken to by their own bosses can be appalling. The "SLT Newbie" parody account on SM is very close to the truth.
Remove league tables, they help nobody and tell you almost nothing about a school.
Remove Ofsted inspections as they are and put in place the old style HMI visits which were longer term relationships and more supportive and less instantaneous judgement based on snapshots and data.
One exam board per subject. Stop reinventing the wheel.
Pay rises to put all public sector workers back to 2009 levels.
Performance management to be less about criticism and far more about personal and career development. Lesson observations must be supportive of development, not not picking for the sake of it.
Re-establish pay superiority for experienced, long service teachers. Needs to be value placed on great teachers in staying in the classroom and not climbing the greasy pole.
There's loads more but I can't think of them right now.....