Dr. Who has been around since television as black and white and then got new look back in 2005. It’s been a huge success ever since and the books have been rolling out en mass. There is a difference between the writers of the books and the writers of the television show… they are completely different people.
You’ll have the same group of talented writers put together season after season of the television show, meeting every week to discuss plot lines and how all the episodes are going to fit together. Book writers are contracted outside the realm of the television show. Publishers pick out the writers based on who they know and submission acquired from fans who happen to be authors as well.
The books can be completely different than the television show and should never be considered canon. The books can featured people that died on the show or completely contradict what happened on the television episodes. This is especially true of Doctor Who because you’ve got 50 years of stories to draw from.
Books are static. Once they are out, nothing changes. So, if a book was written before a specific episode aired that killed off an important character, then that person may show up in the book after a point where he died…then again, he is a Time Lord after all.