I've been having many issues with this and cannot progress the main storyline due to a couple of glitches.
When the battle started with Alduin, things were going fine until I realized it was about ten minutes into the battle and he hadn't lost a sliver of health. When my companion died, I decided I'd look into the issue and realized that I experienced an old glitch where Alduin becomes invincible. It was suggested to just reload and try again, so I proceeded to do that.
However, my issue now is I am stuck at the cutscene where the Nords yell "Alduin approaches!". Nothing progresses after that and everyone just stands in a ready position. I've tried reloading several times after that, waiting 24 hours (in game) before reading the scroll, fast traveling, etc. Nothing works, and I'm still stuck at the cutscene. What do I do?