Thanks Erik and Peter for your replies.
Since there are no posts about aikidoka who have been attacked, tried to defend themselves using aikido, and failed, I can assume the following reasons:
1. Aikidoka are never attacked or get involved in fights.
2. Aikido always works.
3. Aikidoka don't like to mention their failures.
4. They just simply died in the attack.
And Peter, I think there is a big difference between dojo training and real life threats. I think the immediate danger and the adrenaline would create a situation where you become very alert and wouldn't mind harming your attacker in any possible way.