For cards like Void Seeker and Stupefy, do you still draw a card if the opponent retreats the targeted unit?

Ruling: Yes, you still draw the card. The spell resolves even if some or all of its targets become illegal.

Nuances:

• Only instructions that specifically need or refer to a target can mistarget
• Other effects on the spell (like drawing a card) still resolve normally even when the target becomes illegal