Yes, if you exit out you will restart at the beginning. If you got to that point with very few revives then it probably makes sense to restart, but since you are 3/4 of the way through I would probably consider just sucking it up and whittle him down even though it costs you a bunch of revives.
I’d continue from there. If you don’t take blocked hits, I think guardian should work, but he won’t be phenomenal. I personally would rather not spend the 2 hours to get back to that point, but that’s your decision if 2 hours or a hand full of revives is more worth it to you.