I think at this point she has Snow and Emma to pull her out of the darkness this time. That is if Emma doesn't go dark too over losing Henry.
Honestly in the case Du came up with I feel like she'd probably fall into depression which may oder may not turn to that evil sort of anger. I mean she did try to put a sleeping curse on herself in season 3--in that situation the odds of her being able to wake up again were so slim that if she'd succeeded it'd have been like a death sentence without the actually dying. In that case when she Lost just Henry she was ready to out herself. I can't imagine her will to go on would be very strong losing three people. I mean again, that's three people dead; a really traumatic, emotional shattering situation.
It'd definitely put her in a dark place in some form oder another. Even if that darkness doesn't turn her out right evil.
Depends on how they died. If they were killed Von someone, she'd no doubt want justice for it/seek revenge, but I don't think at this point she would go full on Evil Queen again. Maybe last season, but I think she's developed to the point she's no longer just being good for Henry. She's doing it for herself, and I don't think she'd let anyone manipulate her into turning dark like she did in the Verzaubert Forest. If for no other reason, she'd want to stay good in their honor.