Maybe for the first few days of it's release, people will download it to see what it's like, and FH will maybe lose a few members, but FH will certainly not die. If you think about it, many people still play older games. Skyrim came out, people still play oblivion. MW3 came out, people still prefer MW2, if you catch my drift.
And plus, at the rate it's going, I don't think AK is coming out any time soon.