i can't say much for Adidas -- i have some friends that wear them, but they're not gung-ho about it, and i don't think they'd be all that bummed if the ST program went under (esp since the difference between ST and regular seems pretty negligible). but Nike SB? along with Vans, definitely the most popular brand i see on people's feet when i'm out skating. and as the popularity of the Dunk has waned slightly, they've successfully branched out into other shoes (Blazer, Blazer low, P Rod 2, Classics, etc). they're still hot with both the skate crowd and the fuckin streetwear crowd. plus they've got the 6.0 program to boost their bottom line (i'm sure ripping off their own designs is pretty cheap), assuming it's doing well (i don't actually know, i never go to the suburbs). on top of that they still have arguably one of the best teams in skating right now, who all seem genuinely stoked to be there.
the economy might be in the shitter (although i don't think it's nearly as bad as people think it is), but Nike SB isn't going anywhere.