OK, I'll kick this one off...
Firstly you will need a trigger to tell the site you're dead. How to do this is the hardest part! Possibly you have to log in once a week to verify, but ultimately you'll need some failsafe's in place otherwise you risk worrying friends and relatives with your premature news.
Either a Extension utilising a Session hook that runs upon each view of your site then does a check to see if you've been about, or a cron job that calls an ACTion URL (so triggering a module to do the pulse checks).
You could then have a database table, custom user field or update the config file to set a global variable. Obviously if you've gone down the custom database table route, you'll need an additional extension/module/plugin that either pulls that information or sets a global variable to be used in any template.
For your channel "off" scenario, you just have conditionals, whereby your normal news/blog would utilise channel="X", and then either via a parent embed passing it or a simple conditional utilising the global variable, you add the death channel to the parameter, e.g.
channel="1{if dead}|2{/if}" or channel="{if dead}2{if:else}1{/if}"
...or if passing via an embed:
{embed=blog/listing channelParam='channel="{if dead}2{if:else}1{/if}"'}
Regarding: "Per entry set to single member", I'm not sure which add-on you're referring to, but you could do this simply, by assigning the individual to receive the message as the author of the entry. Then when {if dead} display all entries by the current logged in member (if no message for that member, nothing is displayed).
If they already have access to the EE Control Panel, you can hide the entries or channels using this add-on http://devot-ee.com/add-ons/entry-access.
"Daily verification emails", touched on already above, but the easiest method would be to utilise the last visited status of your account and if you haven't been about for a couple of days, then raise the warning flag. As mentioned, either a cron triggering an ACT url and module, or an extension triggered by the session hook (only works if you have a popular site!). Your extension or module could then trigger an email to get you to login into the site. Or if you want to be lazy, you could have a hidden template URL that triggers the email for you: http://devot-ee.com/add-ons/email-from-template.
The 3rd tier of rigor mortis verification would be the same email trigger as above, possibly after the time check has triggered again but after a longer period of time. The difference being that you'd need to get the relative/friend to click on a link (ACTion URL again) that either confirmed you'd popped your clogs, or your heart was still beating.
Granted the 3rd level of checks may counter this, but the biggest problem would be false trigger due to prolonged time away from the internet, or what if there was a problem with your host going down for a period of time, coming back up, and all the triggers firing at once due to the time delay.
RIP.
