It is very easy to kill the yeast with heat. The temp to touch of the must should be only barely perceptible as being warmer than your hand; if it is anything near the temperature of "bathwater" or warmer, you may have killed it.
Don't dump it ... re-add yeast. Even if you don't have more wine yeast, in the interest of salvaging the batch just add bread yeast (which is really just a mixed strain yeast). The taste won't be as good as with a more suitable yeast but it will be drinkable ... anyone who's made JAO (Ancient Orange mead) has used bread yeast with success.
If the existing yeast was ok ... then I'd go back and heavily re-aerate. Also if you didn't add any nutrients already and you have some on hand, I'd dose it. If you were a lot further along in time, aeration becomes more risky with regard to the development of infection.
If it's in an open top primary, aerate by giving it a vigorous stir (a stir that produces froth) for a good 4 minutes straight. If it's in the gallon jug you could shake the jug vigorously while periodically taking the cap off the top to let air in (or removing your hand from the opening etc) ... again, do this for about 4 minutes.
But really from what you said, I'd say the money was on that you killed some or all of the yeast.
As noted though, waiting a bit longer may let any surviving yeast multiply ... it may still work.
