Surprised that nobody suggested
Ask yourself the question about why he burned the friendship and let it remain burned for so many years, and then comes back now.
Does he feel guilty?
Does he want you to absolve him of his sins?
Is he doing this so you won't feel guilty when he goes?
Is he doing this because he wants you to feel guilty after he goes?
He's not your friend, he hasn't been in a long time. Send him a nice note, wish him well and move on. Him getting cancer is not your fault. If he missed your friendship so damn much over the last what 15 years, he would have done this a heck of a lot sooner, but he waited until mortality hit him in the face. He didn't care about you or your friendship and that's why he was willing to burn it over money.
So don't feel guilty when he goes, he wasn't your friend anymore, and you have nothing to do with his current mental or physical state.