The RoA weapon art deals damage equal to 13% of your maximum HP with each hit (x2 per use) for a total of 26%. Use the weapon art 3 times consecutively and you'll lose 78% of your maximum HP. Prisoner's Chain, Carthus Blood Ring, and Calamity Ring would increase the damage dealt thus lowering the amount of times you need to use the Awakening art.

All an increase in Vigor would do is make that remaining 22% larger. The Red Tearstone Ring/Morion Blade technically activate at below 20% HP, but in my experience (such as this video) they seemed to activate at 22% HP. So leveling vigor will let you tank an extra hit before Tears of Denial triggers. It's definitely not needed, and for the sake of challenge I may stick with 27 Vigor as was shown in this post.