Fallon is an american posterboy, I really doubt they give him the boot. Hes not trying to replace Conan either, he's doing his own thing, and he's a geek, says he wants to do a lot on videogames/techy stuff (like the palm pre that was on earlier this week).
I admit I miss Conan too though, nothing will ever be like his show. I'm anxious to see his new show. Shouldn't be too different