How about he be tried and punished in accordance with the laws on the nation he committed his crimes in. Typical poaching punishment is what? 2-5 years in prison? Go for it. 2-5 years of prison in Africa seems like a good idea.
If this was a first time hunt for him, maybe some leniency for ignorance. But he is far from that, having dozens of big game kills under his belt. He knew what he was doing and most likely was aware of the issues surrounding big game hunting. Saying he thought he was on a legal hunt is just saying, "Not my fault, not my problem".
What's worse was that it wasn't a clean kill, so that lion suffered with an arrow wound for at least a day. Sickening.
This person is a dentist. I personally would not ever feel comfortable knowing that the person working on my teeth derives happiness from the stalking and ultimately killing of big game with an arrow.
Perhaps a poetic justice for this person would be that he finds himself weaponless and facing the predators he has killed on the open tundra.