So if her brother doesn't kill her do they live forever?

It would stop the time loop. So no?

I think it's fated to happen regardless and her life is supposed to end at that specific time point, so even if Ewout doesn't mean to kill her, he'll either accidentally still do it, or something else will kill her in his place at that same point. I think that's what Kirsten was trying to explain with the magic loop. It's a fixed time point and the condition that the magic relies on so it'll happen regardless of their efforts

Damn, Kirsten the first done goofed up.