If WTI goes below $85 and stays there, all bets are off for the stock market because the world will have slipped back into depression. Oil begins to be unprofitable to produce at that level, supply drops and the price works its way back up.
Otherwise, if it just dips below $85, it will just be a trading blip, which will certainly pull down energy stocks in the short term, but make no difference in the long term. Just routine supply and demand, with the usual, predictable, energy stock trading overlay. Canaries in the coal mine.