One of the biggest weaknesses of a Simulacrum is its susceptibility to Dispel Magic (as the duration says "until dispelled"). So, dispelling a Simulacrum "kills" it in some way.
The Death Ward spell protects against the first effect that would kill the target.
Does the Death Ward spell protect a Simulacrum against the first Dispel Magic that would "kill" it ? I can see a case for both answers, hence why I'm asking here.
Best Answer
No, dispel magic does not cause HP damage. Disenchanting something is not the same as killing something.
1. No damage is dealt
Your combo works off the following interaction.
The simulacrum spell description says:
The description of death ward says:
Dispel magic deals no damage. It simply removes the simulacrum spell from the target. Sequentially, the simulacrum would revert to snow / ice and melt instantly. Its HP never hit zero as a result of damage.
The same could be argued that you could disenchant a construct and it would stop moving. Any damage to the structure of the construct would remain persistent. If you were able to animate it again - it could be argued the re-animated construct would could have the same number of HP it had before being disenchanted unless time was taken to repair the construct in some way.
2. The simulacrum is never actually killed.
Another part of the death ward description says:
The simulacrum is never actually killed. It is dispelled. Again reaching up to my construct example from before - the construct's form still persists without its enchantment, but it isn't outright killed. Neither dispel magic nor ending a spell is a specific death effect. It creates a death-like effect once it's disenchanted.
Additionally, summoned creatures (Summon Monster and its variants) that are dispelled aren't killed either, they are dispelled. And do not trigger necromancy like effects such as Dark One's Blessing (warlock) or Grim Harvest (Wizard).
Relevant Topic: What happens when you target dispel magic at a summoned creature?