Everything is on the steem blockchain. It is decentralized. Steemit.com is just like a TV set that tunes into the steem blockchain and reveals it a certain way. The steem power and such is not tied to steemit at all.

As long as there are witness nodes still running then there will always be ways to get at the data and currency.

I'll cover currency and such more in another tutorial I write very soon. I've written some in the distant past, but enough time has passed, new things have come up, etc that it is worth making a new post.

EDIT: busy.org is a completely different TV set tuning into the same data. So if steemit went down, and witness nodes were still running then busy.org or a place like it would facilitate other ways to get to your wallet.

Next time steemit lags, go check out busy.org. They usually are not lagging at the same time because, it isn't the steem blockchain that is lagging. It is just the website people visit to view the blockchain that is likely laggy.