Does Zhonya's trigger heal the unit and remove Might debuffs?

No, Zhonya's Hourglass does not remove might debuffs.

According to RiftJudge FAQ 1357 and RiftJudge FAQ 11305, when Zhonya's Hourglass saves a unit:

• Damage is cleared: The unit is healed (as stated in the card's text).
• Debuffs/Buffs are retained: Any existing modifications, including might debuffs (like those from Stupidify), remain on the unit. They do not reset or disappear.

Additionally, per Rule 453.1, a Recall effect specifically does not affect buffed or debuffed status. The unit is moved to your base and becomes exhausted, but it remains otherwise modified exactly as it was before the death event was replaced.