Eidolon Question

So I am currently playing an Summoner and And my Eidolon Has Just recently been slain. I know that i can bring him back at half heath in a day. My question is if i give the Eidolon Fastregen Could he be at Full health when he gets back, or would it not kick in until he gets summoned.

Thanks

Not until he's resummmoned. You're pretty much bringing him back into existence the first time you summon him that next day.