There's a reddit thread that specifically addresses how the mechanics behind Living Dead work. (http://www.reddit.com/r/ffxiv/comments/3...lly_works/)
To sum it up, if you die during Living Dead, you get healed to full and you get a debuff, as Gegenji mentioned. What's not specific in the tooltip is that you then need to be healed for an amount equivalent to your maximum HP in order to remove the debuff. Otherwise, if the debuff ticks down to 0, you die anyway. The trouble is that any amount that qualifies as overhealing does not count towards this maximum HP value.
Let's refer to some examples. DRK, 15k HP.
Example 1:
DRK is sitting at 3000/15000 HP and pops Living Dead. A big hit comes through, "killing" the DRK. leaving them at 1/15000 HP. WHM casts Benediction on DRK, bringing the DRK to 15000/15000. This has only healed the DRK for 12000. The DRK needs to take additional damage so that the WHM can heal another 1 HP in order to remove the debuff. Once that happens, debuff drops off. If the DRK received no additional heals after the Benediction, they would have died when the debuff ticked to 0.
Example 2:
DRK is sitting at 3000/15000 HP and pops Living Dead. A big hit comes through, "killing" the DRK. leaving them at 1/15000 HP. SCH hits Lustrate three times in a panic, for 6000 HP per heal. That brings DRK to 6001/15000, then 12001/15000, then 15000/15000. The debuff does not fade because the total HP healed amounted to 14999 HP, as 3001 HP from the last Lustrate that hit for 6000 HP counted as "overhealing". The DRK will have to take additional damage so that the SCH can heal 1 more HP without overhealing. If DRK and SCH don't meet this requirement, the debuff ticks to 0 and the DRK dies.
To sum it up, if you die during Living Dead, you get healed to full and you get a debuff, as Gegenji mentioned. What's not specific in the tooltip is that you then need to be healed for an amount equivalent to your maximum HP in order to remove the debuff. Otherwise, if the debuff ticks down to 0, you die anyway. The trouble is that any amount that qualifies as overhealing does not count towards this maximum HP value.
Let's refer to some examples. DRK, 15k HP.
Example 1:
DRK is sitting at 3000/15000 HP and pops Living Dead. A big hit comes through, "killing" the DRK. leaving them at 1/15000 HP. WHM casts Benediction on DRK, bringing the DRK to 15000/15000. This has only healed the DRK for 12000. The DRK needs to take additional damage so that the WHM can heal another 1 HP in order to remove the debuff. Once that happens, debuff drops off. If the DRK received no additional heals after the Benediction, they would have died when the debuff ticked to 0.
Example 2:
DRK is sitting at 3000/15000 HP and pops Living Dead. A big hit comes through, "killing" the DRK. leaving them at 1/15000 HP. SCH hits Lustrate three times in a panic, for 6000 HP per heal. That brings DRK to 6001/15000, then 12001/15000, then 15000/15000. The debuff does not fade because the total HP healed amounted to 14999 HP, as 3001 HP from the last Lustrate that hit for 6000 HP counted as "overhealing". The DRK will have to take additional damage so that the SCH can heal 1 more HP without overhealing. If DRK and SCH don't meet this requirement, the debuff ticks to 0 and the DRK dies.