Pretty sure he died from his wounds. Mista did try to aim for non-lethal areas, but that was before they just left him behind to bleed out. Actually, I'm surprised the gang (especially Mista) was so okay with just leaving Bruno's body to die. But I guess they didn't really have any other choice, and stopping Chariot Requiem took priority.
- - - Updated - - -
That scene really showed what an absolute irredeemable scumbag Diavolo is though. Doppio is literally the other half of his soul, someone whose been with him since birth and is completely devoted to insuring his success and victory. If there's anyone Diavolo could be expected to have a genuine bond with it'd be with the guy whose literally, metaphysically part of himself. And yet, once he's no longer useful Diavolo heartlessly tosses him aside just to save his own ass. I don't think it's a coincidence Diavolo had to destroy "the light of his soul" to beat Chariot Requiem. In more senses than one, he sacrificed the only bright and decent part of himself to further his ambitions.
is gone, now onlyDoppioThe pure innocent boyremains.Diavolothe demon