Does the damage from Teemo defending revealing hidden cards resolve before combat might dmg goes through?

Yes. When Teemo, Strategist triggers while defending, his ability resolves before combat damage is dealt.

According to the Riftbound Showdown Timing and related FAQs:

1. Triggered Ability: When Teemo is revealed as a defender, his "When I Defend" ability is placed on the chain.
2. Chain Resolution: Players have an opportunity to play [Reaction] cards. Once the chain resolves, Teemo's ability triggers, deals damage to the attacking unit, and the revealed cards are recycled.
3. Lethality Check: If this damage is sufficient to kill the attacking unit, that unit dies immediately.
4. Combat Damage Step: Combat damage is only calculated and applied after all items on the chain have resolved. If the attacking unit was killed by Teemo's ability, it is already in the trash and does not participate in the Combat Damage Step.

As noted in RiftJudge FAQ #2687: "Teemo's ability resolves and deals damage before combat damage is calculated or applied, which can kill the attacking unit before it deals its combat damage."