The idea that you are alive “now” but will be dead “later” is irrational. Time is just a persistent illusion according to relativistic physics. You are alive and dead, period. A little knowledge is a dangerous etcetera. For one, it's like saying that relativistic spacetime proves New York isn't east of LA, but instead there are NY and LA, period. For another, if he really believed this then he wouldn't be able to function in society or make any plans at all.

Ditto a meat replica But aren't you always a meat replica of any past version of you? If he feels this way then he has to bite the bullet and recommend you quit your job, because you're working hard but it's only a meat replica that will recieve the pay for it.

Many worlds It's not making "another one", it's "A lot more". "Not many" + "A lot more" = "A little more than that". He's making Zeno's mistake here, thinking that just because there are infinite numbers between 0 and 1 you can't get to one, and it's meaningless to say that 10>1 because that's just 9 + infinity and you can't add to infinity.

Now, how does he donate? Does he give a good amount to actually useful charities (ie Villiage Reach, NTD treatments, etc) and you're trying to shift him over to SIAI and other such high risk charities? That would be pretty tricky as it's hard to get a grip on the actual value of SIAI donation. E=(A Lot times very small delta p) per dollar isn't super convincing sell to me when compared with E=(1/7 years of schooling + 1/10 years of healthy life) per dollar. I am not signed up for cryonics, mostly because my nation has no cryogenic facilities and therefore I don't think my brain would fare too well prior to vitrification. However, I would sign up if there was a nearby storage facility, especially since I have no current use for the death part of my Death, Terminal Disease and Permanent Disability insurance.

What I think could be useful is explaining cryonics as an extension of acceptable practices. He'd probably go under anaesthesia for life saving healthcare, and would probably approve of someone being put in a medically induced coma (I think it's generally to keep them stable before surgery but IANAD so do your research first). Explain Cryogenics as effectively a way of sustaining an effectively continuous life to the point where it can be treated and hopefully given a better chance at longevity.