The writers and producers of "Fast & Furious 7" are working frantically (I assume) in tweaking the script to accommodate the tremendous loss they've been dealt, while honoring both the character of Brian and Paul Walker's final appearance in the franchise. Being a writer, I couldn't help but ponder the course of action they'd take.
Paul was only able to finish about half of the scenes he was supposed to do. Therefore, I'm thinking the start of this film may very well begin with a funeral--Brian's (though it's not explicitly said). Then the film will move into the initial storyline, with Paul featured prominently, and then the bad news happens midway--the plan was botched, and they lose him.
The film then takes us back to the opening (or shortly thereafter), and the team makes the decision to avenge him, and the story picks up from there.
Just a thought. No clue which route they'll take...but clearly, it's been on my mind.