At least online - I've never heard it in real life! I've come across posts claiming that the nazis 'unalived' the jews, and another where a woman with schizophrenia 'unalived' her children! It sounds so incredible disrespectful. Nothing else about the posts read like they were trolls or anything, just perfectly factual. I don't see what possible benefit there could be to using that (bizarre!) term rather than 'killed'?