Question is whether fans of the TV series will have become as invested in Rob and his northmen as the book readers were. They freaked out about Ned Stark because he was the biggest star in season 1 and the story revolved around him. But with so many other storylines now I don't think we'll see as big of an uproar over Rob getting axed
Personally I'll be saddened most by his wife having zero role to play over Rob's death itself