With luck this would work. I think a lot of people who emigrated would not necesarily bother updating the postal address details, so this email might just remind them to do the update.

I imagine getting them to provide a proof of new address (which I think is what Hetzner requires from all customers) would be enough. On the other hand, if they just close the accounts for having lived in Russia at a certain point in the past, that would be quite shitty.