I believe you are misunderstanding how Unity works. The damage is split, so you will still take the damage while he cannot die from any damage suffered.

For example, you both have 100 life. You get hit for 100 damage. You take 50, your follower takes 50. You follower then gets hit for 25 because you left them behind. They have 25 life, you have 50 and warps to catch up to you. You take 60 damage. You take 30 and they take 30. It would put them at -5, but they stay alive because of the relic. You take another hit for 100. You die because you now take 50 damage thus putting you at -30.

I believe you are misunderstanding how Unity works. The damage is split, so you will still take the damage while he cannot die from any damage suffered.

For example, you both have 100 life, and you get hit for 200 damage. Both you and your follower would take 100 damage each. Your follower will not die because of the token, however you will still die because you have no item to keep yourself from dying (because there is no such item).