do pikmin go to heaven when they die

They used to. But Hocotate Freight discovered they could harvest the souls of fallen Pikmin to power the infernal engines of the galactic armada they purchased with the profits from Earth.
Yeah, after the events of Pikmin 2, the Hocotate Freight President realized that a source of vast wealth like Earth was too great to allow other companies to exploit. So he conquered the planet, forcing mankind to kneel before diminuitive masters and mass-produce random trinkets to avoid extinction at the hands of an interstellar megacorporation. Those who refuse to kneel before the Hocotate Consortium (as it is now called) are torn limb from limb by Pikmin in what has become the only form of entertainment legally allowed on Earth. Olimar has become the decadent and grandiose Emperor of Earth, while the President rules Hocotate, and Louie, forced into hiding after his dark secret was revealed, now leads the rebel forces in a desperate struggle for freedom.
It'll all be explained in Pikmin 3.
