It might just be easiest to postulate an immortal person and obfuscate the process entirely.
Also, I am trying to come up with a quick test to distinguish passive deathists from active deathists - ie, who would refuse an offered immortality potion, and who would vote against funding to develop an immortality potion? Who would say "I don't want to live forever" and who would say "People shouldn't live forever"? Arguments need to be tailored in different ways for these different types. Something like "How about you take the potion, and then if you actually do wake up one day and want to die, you can commit painless suicide?" for the passives and your "Would you vote for a policy of artificial death?" for the actives.
Last Wednesday (2010 Dec 01), BBC Radio 4 broadcast a studio discussion on the question: "should we actively try to extend life itself?" The programme can be listened to from the BBC here for one week from broadcast, and is also being repeated tomorrow (Saturday Dec 04) at 22:15 BST. (ETA: not BST, GMT.)
All of the dreadful arguments for why death is good came out. For uninteresting reasons I missed a few minutes here and there, but in what I heard, not one of the speakers on any side of the question said anything like, "This is a no-brainer! Death is evil. Disease is evil. The less of both we have, the better. There is nothing good about death, at all, and all the arguments to the contrary are moral imbecility."
Instead, I heard people saying that work on life extension is disrespectful to the old, that to prolong life would be like prolonging an opera, which has a certain natural size and shape, that the old are wise, so if we make them physically young then old people won't be old, so they won't be wise. Whatever cockeyed argument you can construct by scattering into a Deeply Wise template the words "old", "young", "wise", "decrepit", "healthy", "natural", "unnatural", "boredom", "inevitable", "denial", I heard worse.
If I can bear to listen again to the whole thing just to check I didn't miss anything important, I may write something on their discussion board.