You are wrong. They will have the same ending as the books, just the paths towards it are different.
I guarantee you that Martin will do a different ending after seeing how D&D do theirs. Even if he doesn't do it out of spite, the sheer volume of book characters who have no equivalent in the show (or who died early) means there's no way the state of the world and the core cast will be the same whenever Martin finishes the books.
Will there be commonalities? Absolutely. But the endings will be different. Especially considering there's still at least two more books to go.