If you were talking about Jordan I'd agree. However, Martin can end entire side stories by killing people. Daenerys could return in a leaky rowboat with a Dothraki maid and nothing more and still become queen because all other pretenders are dead through intrigue, disease, Others, whatever - you name it.

In fact, if Martin follows the Wars of the Roses (which he has loosely), you need to remember the two successful invasions that no one thought would succeed - Edward IV and Henry Tudor (Henry VII). Both landed with armies that were expected to lose in terms of size and strength, but both won England.