99% of the time i play female.
When i first got the game I tried every thing I could think of to get Alistair to agree letting Loghain become a warden and kill the arch demon but it didn't work. Worst option was he loves you but leaves and never comes back, so i accepted it and did the DR or one of us died. Then I played a character who romancd Zev and had Alistair marry Anora. He fussed when Loghain became a warden but didn't go off and get drunk. After Loghain died he said that I was right. <sigh> Friendship was more important than Love.
Was Alistair hardened when you were romancing him?
The only way to have Alistair stay when recruiting Loghain is by having him marry Anora and to do that he has to be hardened.
And this also works when you are romancing him. I just tested it a few minutes ago and it only took one persuade check.
This also ends the romance. Which is totally understandable.
I don't know what he says after defeating the Archdemon, but I suppose its the same dialog as you get when you were friends.
He's not okay with it, but he understands it. Depending on how you read it, you might have become friends again in Awakening, or maybe he still hates your guts and is just being polite.
ON TOPIC.
It depends on who I'm playing. I actually like Loghain and if you could get both Alistair and him to stay in the party, he'd probably always live.
But since that's not possible, he usually dies. The reasoning being: The joining is often fatal. If I recruit Loghain and he dies, I've lost one Grey Warden and gained nothing. If I kill Loghain, I get to keep Alistair and lose nothing in the process.
When I recruit him it's usually because I don't want to do the Dark Ritual, but still want to have Alistair live. Or if my character hates Alistair and sees no loss in losing him. Or I have a male Cousland who wants to keep his father-in-law.
But if someone hasn't tried it, I would definitely suggest sparing Loghain and then talking to him in camp and checking out some of his party banter. He's surprisingly charming when he isn't going on about the Orlesians and he offers some insight on Anora as well.