First, the story sucked so much. The idea was good, but the ending was shhit.
Second, it was not a heat wave, it was a supernova that caused the sun's magnetic field to become disrupted, in which a solar flare with the height of more than 93 million miles kills all life on earth.
Third, it will happen. It is one of the natural phenomenon that can be Armageddon. Others include giant asteroid, gamma ray bursts, etc.
Sun does not end in a supernova, it's not big enough. Supernovas from far away can cause magnetic field disruptions in our Sun, causing havoc. If the supernova reaches the Sun with enough magnitude, we are doomed.