Yes, but it's not likely. Even with Lanfear's Shield, he was stronger than an average Aes Sedai, and we've seen Moiraine and other Sisters react very quickly to sudden threats.

Not really knocking your theory down, but we've seen too many weaves and effects described as complicated be woven in a heartbeat to really think an assassin holding a knife could kill Asmodean with one blow without reprisal. Moghedien, for example, was struck with an arrow by Birgitte and still had the willpower to trigger an effect in moments before Birgitte, a heroic individual and seasoned archer, could ready, aim and fire.