I have a 2 might unit. It gets 1 damage done by a spell. Then stupify. Is it dead?

Yes, the unit dies.

The unit starts at 2 Might with 1 damage marked on it from the spell. When Stupefy resolves, it reduces the unit's Might to 1 (minimum of 1). During the next cleanup, the game compares marked damage to current Might — since 1 damage ≥ 1 Might, the unit is killed (Rule 143.2.a).

This is the same interaction confirmed across multiple RiftJudge FAQs (#4751, #2426, #1332): damage and Might are tracked separately, and reducing a unit's Might while it has damage marked can cause it to die at cleanup even though the damage came from a different source.