Many folks on this show could get the nomination, so I will break it down into Civies and LCN/OC Members:

Civies:
Tracy - Simply "disappeared" because she set Ralphie's temper off and left behind a little child and the manner that she left was brutal.
Waiter - The waiter that confronted Chris and Paulie over the small tip, again he left a family behind
New Hampshire Guy - He confronted Vito about the car accident and paid the ultimate price.
Sunshine - Gunned down by a bunch of knuckleheads
Truck Driver - The truck driver that got killed by that stray bullet.

Connected Guys:
Eugene - Caught between two worlds, serving two masters, couldn't deal with the stress, took an early exit.
Gigi - Literally couldn't take the stress
Bobby - At the heart of it, he was a nice guy and humble and left behind his kids to the clutches of Janice...
Beansie - Left in a wheelchair and had to take a vow of silence for Richie of all people