When Paul Walker died halfway through the production of Fast & Furious 7, most people mourned not only Paul as a person, but also his character in the movie, Brian O'Conner. The ending of the film worked to give the character a fitting send-off and dedicated it to Walker.
They filmed the scenes that wrote off his character with Walker's brothers Caleb and Cody. It was crucial to involve them, and rework some of the narrative, so that the films could be completed. According to Caleb Walker, however, their involvement doesn't end with that movie and there are plans of bringing Brian back.
Caleb Walker, chatting to Entertainment Tonight, said that “I had a phone call with Vin [Diesel] for about an hour and we really discussed this a while back. He wanted [our] blessing.”
Diesel had asked if it “would be acceptable to maybe bring Paul’s character back… to really kind of let his fans know he’s still out there,” Caleb Walker revealed, noting that “Universal wants to make sure to be respectful of Paul and his image too, and his family.”
The plan hasn't been revealed any further as to what will happen with the character. It is unlikely that Universal will recast the role, so Caleb and Cody could still be involved. That would certainly make it easier on the family.
We'll keep you updated.