A tailed beast bomb was fired straight at him killing everyone including him in the blast radius
The house he was in was hit by the Juubi's TBB, which, as far as we know, killed everyone inside.
He ate a spoiled KFC burger.
You know, this is just a theory... But I think Mabui stabbed him from behind with a kunai and he died.
Then the Juubi blew up HQ so everyone else died too.