I've been reading a lot of different reports on this, and my opinion would be leave him as is but take the necessary precautions.

"Re-introducing Tilikum to the wild would be costly, would include serious risks for the animal and would not guarantee his survival. There is absolutely a risk in keeping him where he is," said Naomi Rose, a marine-mammal scientist for the Humane Society of the United States.

Killer whales in general are highly intelligent species with their own unique personalities. They've also been provent to suffer (as we do) from depression, boredom, anxiety, etc. Stress is a factor too and can harm them physcially as it would us.

Removing him from shows can also heighten his boredom and lead to random fits of rage. I don't believe in putting it down myself, they knew the risks going when they capture/breed/use such large animals.