I think it's too different a scenario. Giles didn't have a personal relationship clouding his judgement like Buffy did to Spike, but he did have a personal relationship with Willow.
So I dont think he'd try to kill her, but I also dont think he'd let her stay there.
He'd send her to the coven, or bind her in her own power again, he wouldn't be stupid enough (like Buffy was) to let her walk around knowing she could go evil at any time. If they couldn't break into her emotion by trojan horsing her with good magic like he did in season 6, cuz she was triggered, they wouldn't stand a chance, he'd know that and he wouldn't be as reckless as Buffy was about it.
I think we'd have seen a similar story where Buffy wants to keep Willow, cuz she is actually the best weapon they have and behind her back Giles tries to bind her or recruits the coven to kidnap her - actually I kinda wish that was the story, it would have been much more relevant to centre that story around Willow as she was in the same position but she actually mattered to the overall story, and it would have been a much better reason for Giles and Buffy to fall out. Would have been actual drama, rather than needless melodrama.