It could indeed be that simple. With inside temps above 100F, your yeast could have succumbed to the heat. All yeast strains have a recommended temperature range. That of K1V-1116 is 59 to 86F, based on manufacturer information.
Killing the yeast outright is probably better than having it struggle through at those temperatures, BTW. Large amounts of fusels and other off-flavored compounds are typical byproducts of a hot fermentation, and yours was really hot.
It may be that your second pitch did not take hold because re-starting fermentations where the must has more than a few % ethanol by volume can be a dicey affair. Let me recommend that you read the Lallemand recommended approach to re-starting stuck fermentations:
http://www.lallemandwine.us/pdf/overcoming_stuck_fermentation.pdf
That may be more than you wanted to know, and you don't need to use the "Pro Restart" products in order to be successful, but the gradual acclimation of your starter to the must through several carefully spaced additions is the only thing that works consistently for me. You didn't say in your note how many additions you made over that 24 hr period.
Even then, it is important to realize that some fermentations just don't get going again no matter what you do.
Or, you could just stabilize this sweet batch with metabisulfite and sorbate and bottle it as-is, or alternately you could blend it with a drier batch to achieve the final sweetness that you're after.
If you do attempt another restart, I'd suggest that you either invest in some pH strips or a meter, and check pH before proceeding. If the pH is too low, nothing that you try will work.