I think that in the case of Glory opening the portals and returning home she completely regains her powers as a god meaning that the Ben half of the Glory/Ben body sharing "arrangement" would be entirely overwhelmed by the Glory half and hence he would be snuffed out of existance.
However, Glory suggests in The Weight of the World that as a god she would have the power to keep Ben, not only alive, but make him immortal, presumably as a seperate entity. Here is the transcript from that ep:
Glory pulls Dawn away from the dumpster, throws her across the alley, then throws the bottle against the wall. We hear it shatter. Dawn crouches on the ground staring at Glory in fear.
GLORY: You can't hurt her and you know it, Ben. (sits down on a pile of bricks) I know it 'cause I feel what you're feeling. Scared. Shh! Shh! It's okay! You don't wanna die. Who would? I don't.
BEN: You can't, you're immortal.
GLORY: Nobody has to die here, Ben. Just let me bleed the girl and go home. Everything will work out fine.
BEN: Do you really believe with all I know that you can trick me?
GLORY: Stop ... and think, baby. We bleed the kid, return me to my seat of power, I become a god again...
BEN: And I disappear.
GLORY: Ooh, unless somebody up there likes you. Give up the girl ... I could like you a lot.
Dawn watches this wide-eyed.
BEN: I won't make a deal with you, Glory.
GLORY: (angry) When exactly did you get stupid? I'm offering immortality here.
BEN: I believe you. That's not the problem. You make me immortal, then what? (walks over to Dawn, grabs her arm and pulls her to her feet) I'd have to kill her to do it and I won't be able to live with that, not even for a day, forget about eternity!
He whirls Dawn around in a circle and morphs in mid-whirl.
GLORY: Baby, baby, baby Ben. (lets go of Dawn who falls to the ground again) Why do you worry so much? When you're immortal, all this crap you've been carrying around inside ... (leans against the wall) the guilt, the anger, the crazy-making pain ... (smiles) Ooh, it all just melts away like ice cream. Trust me. When all this is over I can set you up real nice. I'm making it easy. It's you ... or the girl.
She slides down the wall and morphs halfway down.
BEN: (panting) I can't accept that.
GLORY: Accept it. (chuckles) I'm a god, stupid.
She morphs into Ben again. He stares at Dawn, who stares back fearfully.
Ben gets up, goes over to Dawn, holds out his hand.
BEN: I'm sorry.
Dawn sighs in relief, lifts her hand to take his. Ben grabs her wrist instead.
DAWN: No!
Ben pulls her to her feet and leads her out of the alley.
BEN: Don't make this harder than it already is.
Overhead shot of them from the back. They come out onto the street.
BEN: I'm sorry, I got no choice. It's you or me.
Three minions appear and walk up to them.
However, Glory suggests in The Weight of the World that as a god she would have the power to keep Ben, not only alive, but make him immortal, presumably as a seperate entity. Here is the transcript from that ep:
Glory pulls Dawn away from the dumpster, throws her across the alley, then throws the bottle against the wall. We hear it shatter. Dawn crouches on the ground staring at Glory in fear.
GLORY: You can't hurt her and you know it, Ben. (sits down on a pile of bricks) I know it 'cause I feel what you're feeling. Scared. Shh! Shh! It's okay! You don't wanna die. Who would? I don't.
BEN: You can't, you're immortal.
GLORY: Nobody has to die here, Ben. Just let me bleed the girl and go home. Everything will work out fine.
BEN: Do you really believe with all I know that you can trick me?
GLORY: Stop ... and think, baby. We bleed the kid, return me to my seat of power, I become a god again...
BEN: And I disappear.
GLORY: Ooh, unless somebody up there likes you. Give up the girl ... I could like you a lot.
Dawn watches this wide-eyed.
BEN: I won't make a deal with you, Glory.
GLORY: (angry) When exactly did you get stupid? I'm offering immortality here.
BEN: I believe you. That's not the problem. You make me immortal, then what? (walks over to Dawn, grabs her arm and pulls her to her feet) I'd have to kill her to do it and I won't be able to live with that, not even for a day, forget about eternity!
He whirls Dawn around in a circle and morphs in mid-whirl.
GLORY: Baby, baby, baby Ben. (lets go of Dawn who falls to the ground again) Why do you worry so much? When you're immortal, all this crap you've been carrying around inside ... (leans against the wall) the guilt, the anger, the crazy-making pain ... (smiles) Ooh, it all just melts away like ice cream. Trust me. When all this is over I can set you up real nice. I'm making it easy. It's you ... or the girl.
She slides down the wall and morphs halfway down.
BEN: (panting) I can't accept that.
GLORY: Accept it. (chuckles) I'm a god, stupid.
She morphs into Ben again. He stares at Dawn, who stares back fearfully.
Ben gets up, goes over to Dawn, holds out his hand.
BEN: I'm sorry.
Dawn sighs in relief, lifts her hand to take his. Ben grabs her wrist instead.
DAWN: No!
Ben pulls her to her feet and leads her out of the alley.
BEN: Don't make this harder than it already is.
Overhead shot of them from the back. They come out onto the street.
BEN: I'm sorry, I got no choice. It's you or me.
Three minions appear and walk up to them.