I totally appreciate and applaud the idea of using mechanics I'm not familiar with. If I were that barbarian, I'd be very excited to have died like that.

As a DM, I would enjoy that. But since I put PCs in scenarios where there's a high likelihood of failure, I don't want them to feel like the physics of the campaign has suddenly changed during the last battle.

I've tossed out new mechanics (doom trackers, Blades in the Dark style heists) mid campaign, but I'd prefer not to do that when we're coming to a conclusion.