To put this in really simple layman's terms, you have to think about whether one thing can still happen without the other thing. So in this case, blackouts can still occur even without a heat wave. That is why the statement "if the heatwave abates, then blackouts will not occur" is not the correct choice. Blackouts can still very much happen without a heat wave, think man caused fire damaging the electrical grid, equipment failing, a tree falling on a power line, etc.