You can't just claim he is alive, and not offer proof.

If the Ukrainians had PROOF that he is alive, they would provide it. They know this thing gets bigger every day.

Instead they just want to muddy the waters "Well, you don't have proof that he is dead, so there". Yeah, but when someone is missing, it really doesn't matter if they are dead or not, if they aren't free, and never re-appear!