In theory, it depends if he has a will: if he doesn't, then you would inherit everything automatically. Even if he doesn't, the starting point should be that you'd keep anything that was jointly owned.
If he did have a will and some of his property was solely owned by him, then he could leave that to someone else. If you're financially dependent on him and he had completely cut you out of the will by designating all his assets as just his, not joint, you'd have legal grounds as his spouse to contest the will as not having been sufficiently provided for.
If he does have a will, but he made it before you were married and hasn't changed it since, your marriage revokes the will and you would inherit everything.
So it depends how he has the £1m - if he's got it solely in his name in property, etc, then he can leave that to his children (you could still contest it, but it wouldn't automatically go to you). If it's just cash/shares/etc then legally I think it'd be much more difficult for him to 'ringfence' that from you - but there are many variables that could change that.
I really hope you're okay. I know you say leaving isn't an option, but if you need advice or help at any point at all, Refuge's domestic abuse helpline is 0808 2000 247 and available any time. You can also email [email protected].
And Mumsnet is always good for advice, support, and strength. 