I can't really speculate on a hypothetical situation with so few details.
That said, I would speak up. If Kiddo and my husband have conflict, I do my best to let them handle it. If I feel like things are going nowhere (usually my son is in arguing mode, which is normal for his age), I might intervene because I see that they both need to take a break and cool off. It's never come to the point that I was worried for my son's safety.
If I can't handle my husband's anger, why on earth would I ever think my son could?
Because of my life's circumstances, I know I could leave a bad situation and be on my own because I've actually done it (both with my mom and later, my emotionally abusive ex-husband). If you've never done it before, haven't been truly financially and emotionally independent, that's a much harder thing to face. It can be terrifying-- but for some, being on the other side of that gives us courage to know we *could* do it if need be. For a long time in my life, I also didn't think I could. So, there you go. I can't judge-- I can only know what I would do, or not do, for my kid and myself.