Man... Sorry if I'm being too blunt, but do you expect me to read that? My head hurts from the wall of text.

I read the first few sentences at least, so here's my answer to that

how could steemit.com go down? Is it just a domain that redirects ?

Steemit is only a webpage (and Steemit.inc a company) but Steem is the network that the webpage connects to. Busy is another site that connects to the same network, shows the same posts etc. If Steemit goes down, that's no big deal.

But Busy has an extra feature in the form of a chat. That chat is actually not recorded in the rest of the network.