No issues arise, and the importance of high-level magical healing increases.
A clarification on "how the optional rule's triggers work normally", is followed by "how the addition of your fourth trigger would impact resurrection."
The optional rule has three (recommended) triggers:
- When it takes a critical hit.
- When it drops to 0 hit points but isn't killed outright.
- When it fails a death saving throw by 5 or more.
Instant Death (PHB 197):
Massive damage can kill you instantly. When damage reduces you to 0
hit points and there is damage remaining, you die if the remaining
damage equals or exceeds your hit point maximum.
In this case, you do not make a death-saving throw, and therefore you can't fail your death saving throw by 5 or more, do not roll on the table. Your hit points are dropped to 0, and you are killed outright, therefore trigger two does not apply, do not roll on the table. Your instant death is possibly caused by a critical hit, if this is due to a critical hit, then roll on the table.
If you include a fourth trigger that also enables a Lingering Injury by:
- When it dies.
Then the Lingering Injury may persist after you cast Raise Dead:
This spell also neutralizes any poisons and cures nonmagical diseases
that affected the creature at the time it died. This spell doesn't,
however, remove magical diseases, curses, or similar effects; if these
aren't first removed prior to casting the spell, they take effect when
the creature returns to life. The spell can't return an undead
creature to life. This spell closes all mortal wounds, but it doesn't
restore missing body parts. If the creature is lacking body parts or
organs integral for its survival--its head, for instance--the spell
All mortal wounds are closed. Raise Dead is magical Healing (PHB 197) so it will remove the effects of Limp, Internal Injury, Broken Ribs, and Festering Wounds. If cast at 6th level or higher, then it will also remove the effects of Horrible Scar, and Minor Scar. No body parts are restored either way.
So if you are resurrected by magical healing, then you will remove the effects of Limp, Internal Injury, Broken Ribs, and Festering Wounds. If the method of resurrection is a 6th-level spell or higher, then it will also remove the effects of Horrible Scar, and Minor Scar.
Resurrection will also restore your missing body parts. True Resurrection will replace any damaged or missing body parts.
Spells such as Animate Dead are not magical healing. They are creation type effects, and thus will not remove any of the Lingering Injury effects.
The fourth trigger will make some of the conditions more impactful for characters that die, as you create options that introduce the potential for long-term injuries with this optional rule it appears to be in the line of that intended design. The importance of high-level magical healing increases.