Something I've thought about DRK would be an enhanced Sole Survivor.
If marked target dies under the effect of Sole Survivor, Walking Dead status is lifted.

Note it's not Living Dead, but Walking Dead. Meaning you'd have to actually be under the need for a full HP recovery for this to take effect. Making it not too overpowered, but more importantly bringing DRK into a realistic balance with the other tanks as they are now.
If a PLD or WAR has the need to use Hallowed Ground or Holmgang, they both have options to recover HP during the time they're active. DRK however, has no way to remove it's own death sentence and is 100% reliant on a healer.