depends on your uni policy and other grades. at our uni if you failed your Diss you didn't get an Hons degree but if your average grade was good you could still pass. Read the policy. Can you defer your Diss? I never met my supervisor and I got a first. I can't remember but I think he died. anyway. how long do you have? just gather a bunch of references and cram.
Depends on your uni regs but as dissertations are usually 40 or 60 credits and you typically need 100 credits minimum at L6 to graduate, you probably wouldn't pass the year if you failed it. You would get a chance to resubmit in August though.