I know this is unacceptable and a horrible thing to say
Then why do you even need to ask for advice?
He always says nasty things when he's angry
Seems he has anger issues. Probably could use some help in learning how to control his anger and not say nasty things to you (or anyone else) when he gets angry.
If he decided to get help for me and sort himself would it be a bad thing if I took him back?
Depends. You need to insist he seek help for why he feels he needs to say such things when he is angry. Stay away from him until he does. And I don't mean just until he has one visit with a counselor, but until he is at least a few months into it. Then maybe slowly and cautiously start seeing him again. But make it plain that you will not tolerate another blowup.
All I've written above are my thoughts based on the idea that you seem to be searching for a reason to stay with him. Personally I think you would be better off ending things altogether. There are actually some great guys out there who would never say the things he said to someone they love. What happens when yelling and threatening you isn't enough for him? I'll tell you. He will resort to striking you. Is that acceptable? (Hint: the answer to that is NO)
By the way, out of curiosity, what does your family say about his behavior? Has he exhibited it in front of them? Have you told them about his threats to harm them? Don't you think they should be aware of this behavior?