For example, me being alive could be determined by whether I logged into my machine over the last X days and a certain service ran. If it didn't, only then start bugging me to confirm manually.
Also, as others have already mentioned, I'd have very little trust that such service will still be around when I'll need it to trigger.
Something like scheduled gmail + a cronjob on my local machine that runs once a day and reschedules the email is something I'd imagine could work if I wanted to set up something like this for myself.