combat showdown cleanup resets - might effects and heal all units?

No — the Combat Cleanup's heal step clears damage marks only; it does not reset or remove Might modifications.

Damage is tracked separately from Might, and the Combat Special Cleanup inserts only "Heal all Units" (Rule 466.1.a.1). Temporary Might buffs/debuffs keep their stated duration: "this combat" effects expire at combat end (Rule 466.7.c), and "this turn" effects expire in the Ending Phase's Expiration Step (Rule 317.2.c) — not during the combat heal. So a +1 Might buff from earlier still applies for damage assignment and surviving combat heals the damage without touching the buff.

I noticed multiple unrelated questions. I've answered the first one — please ask the others in separate messages so I can give each one proper attention.