Correct, when Steemit goes down the gutter, Steem may also suffer, but I expect these Steem millionaires will power down in time and move on to some other coins to put their money in. I don't think too many big SP holders look long(er) term, since anything can happen; for instance competition with better tools and a inbuild revenue stream, maybe even from the 'old' world with fiat currency. Bridges need to be build with the old world, and only a few are doing this. Steem shows with their focus on the blockchain and SMT they are not investing in tools to eg onboard brands like Coca Cola and the gazillion other ones using social media for their marketing.