Jesus wasn't a wasteful man. After both of the fishes and loaves mirarcles there were leftovers. Did Jesus want this food wasted?
Joh 6:11 And Jesus took the loaves, and when He had given thanks, He distributed to the disciples, and the disciples to those who had reclined; and likewise of the fish, as much as they wanted.
Joh 6:12 And when they were filled, He said to His disciples, Gather up the fragments left over, so that nothing is lost.
They gathered 12 baskets after the first miracle and 7 after the next. Jesus wasn't wasteful.
If he considered swine acceptable food, he surely wouldn't allow them to be wasted by allowing demons to enter into them and having them die at sea.
That is a stretch considering most of the people he came to didn't consider them a food source to begin with and may be why there was still a herd of them left.