If my opponent plays Sacrifice on the target of my Starcrossed, does my unit still return to my hand?

Yes, your unit will still return to your hand.

In Riftbound, spells do not "fizzle" (fail entirely) simply because one of their targets becomes invalid while the spell is pending on the chain. As long as at least one of the original targets remains valid, the spell will resolve as much as possible, ignoring only the instruction that cannot be performed.

Sequence of Events

1. You play Star-Crossed: You target your friendly unit and an enemy unit. Star-Crossed is added to the chain.
2. Your opponent plays Sacrifice: To pay the additional cost, they kill their own Mighty unit. Sacrifice is added to the top of the chain.
3. Chain State (Top to Bottom):
   • [Top] Sacrifice
   • [Bottom] Star-Crossed
4. Resolution (LIFO - Last-In, First-Out):
   • Sacrifice resolves first: Your opponent draws 2 cards and channels 1 rune.
   • Star-Crossed resolves: It checks for its targets. While the opponent's Mighty unit is now in the trash (making that part of the instruction impossible to follow), your friendly unit remains a legal target on the board. Therefore, Star-Crossed proceeds to return your unit to your hand and ignores the instruction to return the opponent's unit.

This ruling is consistent with Rule 359.3.e.8, which states that if an instruction has more than one target and fewer than all of those targets become unavailable, the instruction will still execute on the remaining valid targets. This is also confirmed by RiftJudge FAQ #10058, #10311, and #10736, which all address scenarios where a Star-Crossed target is removed from the board before resolution.