I think a cool kick to it would be: all damage dealt to you that would of dropped you below 1 hp is stored and granted as a heal when Holmgang ends

So if you pop it and you took at 6k hit with only 2k health left. It drops you to 1hp. When Holmgang ends it would heal you for 4k hp.

Basically bringing it more on par with Hallowed but in a different way requiring more strategy to use.