Depending from the levels of the trust of the characters by the end of the game, some sadder variations of the ending play out.
With Cain absent, and if Bo decides to obey the Major, it's Rachael who takes the punch from the Major's mech to protect Faye, but the hit is fatal for Rachael, whose last words and motivation for such sacrifice are "Human... enough... for me."
With Cain absent, and if Bo decides to take Dan's side, it's Bo who takes the punch from the mech.
In either of the above cases, after the fight with the Major is over, Dan has a conversation with a dying Bo, who asks him for a final cigarette, and dies telling him to protect Faye. The scene plays exactly the same in both cases, taking a different significance in each context: if Bo chose the Major's side, he sounds like he regrets his choice in his last moments.