This causes a bunch of confusion: If your soul is in heaven, and your body is reanimated, what happens? Do you get sucked back out of heaven?

You could bring up the example of induced hypothermia, and then suggest that in that case, the person isn't actually dead, but just in a state of suspended of animation. (They have to be - after all, the opposite would imply that their soul would get sucked back from heaven, and that's absurd, right?) If you can establish that, you can go on to suggest that being cryogenically frozen is a similar state as well.

If you can do this in a way that doesn't suggest you're starting a debate, but rather are curious about their beliefs, that would help. "Say, I ran across this article about something they call induced hypothermia, and I'm a little unsure about whether I should think the patient is alive or dead while he undergoes the treatment. I mean, if he comes back afterwards, he can't really be dead, but the article says that the patient is indistinguishable from someone who is. What do you think?" If they reach the conclusion that the patient is actually alive, agree with that or possibly challenge the position a bit (to make them think of more justifications for it and thus become more sure of the position), then let the issue rest. Only bring up the cryonics connection in a later discussion.

Of course, you have to be able to do this in a way that doesn't seem too uncharacteristic of you - if you've never asked for their thoughts in such a manner before, doing it now is probably a bit suspicious.