Well I am surprised that they said you would bleed - but perhaps in your particular case as you have a thickened lining? I had a slightly thickened lining for post-meno and was not told anything about bleeding and nor did I - after hysteroscopy! Anyway the hystersocopy would check whether, as you say, there are any abnormalities present like fibroids or polyps, so stopping bleeding isn't actually going to tell them that, and as you also say, you have been taking progestogens and other medication to stop the bleeding - but the ongoing cause should still be investigated!
Did you see what I said in my post about an ablation? This is another option for some women.
Also if it was a choice of hysterectomy or Mirena (to control bleeding) then I would definitely go for the latter, at least at first, synthetic progestogens or not - as hysterectomy is irreversible and not without its potential long term issues.
Hurdity x