i was able to bypass the quest that breaks the Main Quest by doing Dawnguard first. However I'm having some serious problems with doing this quest with my VL Mage file.

Where to start? Lets see for some reason I'm getting the bug where I can't damage him after his speech. Regardless if I attack him before the speech or after. So I have to clear my cache/or restart my system. Which corrects that bug. However I run into this bug next.

Alduin i use Dragonrend on him while flying and he gets ****ing stuck in the damn air hovering to the point where I can't do no damage again! So I reload my autosave and bam right back to the first damn bug I described.

So if anyone has some helpful tips on this buggy quest I'd love to hear it. Edit: I was able to finally bypass the bugs after only 45 mins wasted on a boss fight.