To answer the original question, I don't think it's as simple as 'yes' or 'no'. Do I think some parts of it will be changed, oh yeah! But I think they can also use some of it and it will work. It really just depends on when E7 is set. These are things that could be easily explained, and very quickly, it's character development and it happens in movies all the time. If they didn't go though introducing Mara and having her as a character (I'm not saying they will or won't, just giving an example) they could do a flash back, they could have any character talking about her, telling a story/memory, the opening crawl as someone else already said. There are any number of ways to introduce characters that aren't even seen and it's very easy and quick in movie time to do. If those characters are ones hardcore fans are familiar with, that's great and we know a little bit more about them, but that doesn't mean they can't easily introduce them as new characters (Or change aspects of characters we already know, for that matter.) to people who haven't read the books.