If you want to completely start over, yes you'll need to reload a save game from before the point at which you fell. Please note that following the first cut scene where you confront the Warden gal in Adamant Fortress when the dragon appears, opportunities to get a save in can be spotty. My advice would be to save before this point and hope you get a shot at saving afterwards.
You can probably still do the fight with the setup you have. I wound up soloing it on Nightmare difficulty after my party kept dying. Of course I was playing a rogue so Stealth played a huge factor and I was rocking a life drain ring... So depending on what your situation is and how comfortable you feel with the fight, will determine whether you continue or start over before you fell into The Fade.
