If the first target of Piercing Light leaves the battlefield, will the second target still take damage?

Ruling: Yes, the second target will still take damage even if the first target leaves the battlefield.

Nuances:

• The word "then" in card text does not create a dependency between effects - it's essentially meaningless for resolution purposes
• The keyword "to" (as in "do X to do Y") creates a cost-to-effect relationship where X must successfully resolve for Y to happen
• If Piercing Light were templated with "to" instead (e.g., "Deal 2 to a unit to deal 2 to another unit"), then the first damage would need to resolve for the second to happen
• Costs don't target, so in a cost-based version you wouldn't choose the first unit until resolution