709 rides are kinda the luck of the draw on inspectors. Considering your circumstances, (the downdraft) if the inspector that decided you need a 709 ride is the one giving it, you may be in trouble. If you get another inspector who thinks it's pretty much a billshut deal, you'll be OK. I had a couple of my pilots earn 709's over the years, and they both did ok, it was treated more as a formality. If you fail it, or get a real deckhiad for an inspector, you will most likely lose every cert/rating you have. Not a HUGE deal, you'll just have to take PVT/INST/COMM/ME rides again. Get an EXAMINER for this, will cost a few bucks, but most will have some pity considering the circumstances.
What the one guy said about AOPA legal services is probably your best bet. If you can put the ride off until you've had time to talk with an aviation atty, you might be able to get out of the ride if the atty can pull a WX report showing conditions conducive to downdrafts on the day of the incident near the appropriate airport. Two people in a 150 on a hot day with a serious downdraft is something almost any NTSB judge should understand.
Good Luck, both with the situation and your upcoming interviews.