Well, i am also talking about the main choices.
As said, the Warden can made some seriously morally-ambiguous choices and can kill all his companions if he wants to.
Hawke can give up Isabela and Fenris and kill her sister and Merrill (siding with the templar) if she so wishes.
As Inquisitor, there is no way for u to kill Vivienne even if u hate her, banish Cole back to the fade or feed Dorian to the Red Templars. The main choices are not even remotely morally ambiguous.
The Warden can't decide to kill off companions. What can happen is that you can pick one totally insane option at the temple of sacred ashes that will make some party members fight you. There are also options to kill people before recruiting them, but otherwise people turn on you.
The real problem with this in DAO (and DA2) is that some choices jump over the moral event horizon to such a degree that it's hard to conceive why some of the party wouldn't abandon you.
DAI avoids this issue by cutting off your petty evil options and the insane alternatives to quest (e.g. siding with the crazy cave dwelling unwashed hermits).
There's a real debate to be had about the lack of savagery with some DAI content (e.g. execution) but that's separate from companion related stuff.