Oh Endesha.... For those of you who will comment that he should have ran think of this. The lions/lionesses being killed are his family and lifelong friends. He is the future king of the South Lands and he is not a coward- he's doing what he thinks is right. It's his duty.
a bit of script from Bambi II comes to mind:
Great Prince: Try to feel the forest around you.
Bambi: I don't feel anything.
Great Prince: Does playing in the meadow.
Bambi: How do you know?
Great Prince: I feel it in my hooves. If there was danger, they'd know to stomp, and I'd run to them.
Bambi: But wouldn't you be scared?
Must be hard chose between the right thing to do and your duty as leader (at least I think Shenzie act pretty much as the clan leader, even if Scar demanded control over it after Viccha's death) to protect the clan from the madness of a cruel king.
That's why I would prefer to not be in charge of sonething like that in real life, responsabilities are a real thorn in your side sometimes.
I like that even then, Shenzi still would have preferred that Endesha had run away (and likely took Zira with him). It's not that she won't do what Scar told her to, but that doesn't mean she has to enjoy it.
Again, I really don't think she would hesitate or have the same feelings if it was just an ordinary lioness and not Zira, who she knows and might have seen from time to time as she grew up.