Oh they might have missed the initial rush, but not even WoWtcg depends on online players alone. It's a good game, with good looking cards and "free lore" from the online game.

Warhammer card game has interested players from the fans of Warhammer already. Mythic has tied their online prize codes from Red Alert games to conventions and whatnot. In my opinion, Not using codes on those cards would be stupid from FFG and Mythic.
Mythic might get new players from Warhammer fans playing the card game. "Hey, I got this weird card! What does it do? Well, I got it.. might as well see what it looks like in the game.."
FFG might get new players from online gamers. "I just want that cool thingy for my char... it's too cool to miss.. Well.. now that I have these cards, why not try the game.. Hey, I actually like it.. Giev more cards!"

The success of such symbiosis would not be as great as WoWs of course. What does? But you cant deny the synergy.. :)