You know, I really wanted DA to continue into 1926 and the General Strike, but reading up on the 1925 law, I have some sympathy for the decision to stop now! My understanding is that Lord Grantham would have been able to "bar" the entail and create a new will determining how the estate would be inherited from him. I think that this would have required little George's consent, though how that would have worked I don't know. Anyway, Lord Grantham could then could name Lady Mary as the inheritor, or divide it between the sisters (not terribly likely), or donate it to the Royal York Infirmary to spite his mother, or whatever. However, he could also have chosen to do nothing, and the entail would have persisted, at least until 1997 when there were more changes to this law -- or until the next heir decided to end the entail. (My reading suggests that it's a little dodgy that he found it so completely impossible to bar the entail back in 1912 or whatever, but that's a different problem altogether.) Now that I've written this all out, I'm back to wishing Fellowes had decided to tackle this after all... the drama! Anyway, I've mainly relied on Megarry's The Law of Real Property for this.