From The Hollywood Reporter:
Sources say writer Chris Morgan now is at work crafting revisions to the script that Universal execs hope can retire Walker's character from the series using scenes already shot. If he succeeds, cast and crew could be called back to work by late January — but that's a big if.
The other possibility is that Morgan is not able to come up with an appropriate way to write out the character of Brian O'Conner. If that happens, the whole production may start from the beginning, which would be unprecedented in movie history.
According to a knowledgeable source, the studio already has poured about $150 million into the film, a bill that its insurance firm, Fireman's Fund, might have to pay in full if Universal concludes the picture must be started anew. Fireman's Fund declined comment, as did Universal.
I can't imagine the studio would scrap the filmed parts entirely. They need a way to include Walker's death. The problem, I'm guessing, is studio executives want the death to occur near the end of the film, so they can set up a revenge-type plot to launch Fast 8. Which they may not have enough footage for. I bet that's the real hold up.
Regardless, the July 11th release date has been unofficially scrapped.