A Manifestation of Chaos: Extinction Event!
Pathfinder - Rules Clairifications - Races
Remember also that the eidolon does not heal naturally. Just like hit point damage, any ability damage or drain the eidolon has persists between when it is banished/dismissed/killed and when it is resummoned. The exception is an eidolon killed by Con damage (which, if resummoned, would still be at 0 Con and immediately die and vanish); in this situation, the resummoned eidolon is cured of 1 point of ability damage or drain so the amount of damage or drain is 1 less than its actual Constitution score, allowing it to live.
Effects that cure ability damage or drain work on the eidolon’s ability scores when it is summoned.