What would have happen to peeta if finnick was not in katniss and his group

I think that would have been it for him.
His heart did stop, and, like we all know, you are dead when that happens.
Katniss may not have known what to do.

Then he would've died, sadly, because his heart stopped and Katniss didn't know what to do.

he'd be dead..i <3 Finnick!!

I would cry that Katniss no longer has her love and the future father of her children!!!