I don't think that by shutting down SR directly defines bitcoins fall, but it will severely damage bitcoins current somewhat stable economy. A lot more companies adopting it is what will eventually sustain bitcoin. That's why it's necessary that we spread the word as much as we can so that eventually the number of people that support bitcoin outweighs SR's support.
Agreed, but the unfortunate truth is that a handful of black markets adopting bitcoin will have a more significant/positive (stabilizing) effect for the btc economy than a handful of established companies, unless they're really major players like ebay, amazon, paypal or google/apple. In terms of profits, SR is said to return >= ~20M per year, that's fairly significant and means there'll be a constant supply of people wanting to trade via btc.